{"id":590,"date":"2018-01-19T17:12:40","date_gmt":"2018-01-19T22:12:40","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/?post_type=chapter&#038;p=590"},"modified":"2018-03-09T20:41:20","modified_gmt":"2018-03-10T01:41:20","slug":"5-1-gas-pressure","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/chapter\/5-1-gas-pressure\/","title":{"raw":"8.1 Gas Pressure","rendered":"8.1 Gas Pressure"},"content":{"raw":"<div class=\"bcc-box bcc-highlight\">\r\n<h3 itemprop=\"educationalUse\">Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Define the property of pressure<\/li>\r\n \t<li>Define and convert among the units of pressure measurements<\/li>\r\n \t<li>Describe the operation of common tools for measuring gas pressure<\/li>\r\n \t<li>Calculate pressure from manometer data<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idm2965936\">The earth\u2019s atmosphere exerts a pressure, as does any other gas. Although we do not normally notice atmospheric pressure, we are sensitive to pressure changes\u2014for example, when your ears \u201cpop\u201d during take-off and landing while flying, or when you dive underwater. Gas pressure is caused by the force exerted by gas molecules colliding with the surfaces of objects (<a href=\"#CNX_Chem_09_01_Pressure1\" class=\"autogenerated-content\">Figure 1<\/a>). Although the force of each collision is very small, any surface of appreciable area experiences a large number of collisions in a short time, which can result in a high pressure. In fact, normal air pressure is strong enough to crush a metal container when not balanced by equal pressure from inside the container.<\/p>\r\n\r\n<figure id=\"CNX_Chem_09_01_Pressure1\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"975\"]<a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Pressure1.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Pressure1.jpg\" alt=\"The left side of this figure includes a graphic of the earth with an inverted rectangular prism extending from a point on it. Near the top of the image, the label, \u201csquare inch column of air molecules\u201d is connected to the prism with a line segment. This label is also connected with a line segment to a downward pointing arrow at the right side of the figure. Beneath the arrow is a red circle labeled, \u201catmospheric pressure.\u201d A narrow rectangle with a dashed line border extends from the bottom of the arrow vertically through the circle. Directly beneath this rectangle at the lower edge of the circle is a hand with a thumb appearing to be resting on a tabletop. The thumb is connected with a line segment to the label, \u201c14.7 lbs of pressure on 1 square inch.\u201d The red circle is sitting on top of the thumb.\" width=\"975\" height=\"458\" \/><\/a> <strong>Figure 1.<\/strong> The atmosphere above us exerts a large pressure on objects at the surface of the earth, roughly equal to the weight of a bowling ball pressing on an area the size of a human thumbnail.[\/caption]<\/figure>\r\n<div id=\"fs-idm5657392\" class=\"textbox shaded\">\r\n\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/OSC_Interactive_200-15.png\" alt=\"\u00a0\" \/>\r\n<p id=\"fs-idp139792368\">A dramatic <a href=\"http:\/\/openstaxcollege.org\/l\/16atmospressur1\">illustration<\/a> of atmospheric pressure is provided in this brief video, which shows a railway tanker car imploding when its internal pressure is decreased.<\/p>\r\n<p id=\"fs-idm26057840\">A smaller scale <a href=\"http:\/\/openstaxcollege.org\/l\/16atmospressur2\">demonstration<\/a> of this phenomenon is briefly explained.<\/p>\r\n\r\n<\/div>\r\n<p id=\"fs-idm5227120\">Atmospheric pressure is caused by the weight of the column of air molecules in the atmosphere above an object, such as the tanker car. At sea level, this pressure is roughly the same as that exerted by a full-grown African elephant standing on a doormat, or a typical bowling ball resting on your thumbnail. These may seem like huge amounts, and they are, but life on earth has evolved under such atmospheric pressure. If you actually perch a bowling ball on your thumbnail, the pressure experienced is<em> twice<\/em> the usual pressure, and the sensation is unpleasant.<\/p>\r\n<p id=\"fs-idp26888784\">In general, <strong>pressure<\/strong> is defined as the force exerted on a given area: $latex P = \\frac{F}{A}$. Note that pressure is directly proportional to force and inversely proportional to area. Thus, pressure can be increased either by increasing the amount of force or by decreasing the area over which it is applied; pressure can be decreased by decreasing the force or increasing the area.<\/p>\r\n<p id=\"fs-idm32668544\">Let\u2019s apply this concept to determine which would be more likely to fall through thin ice in <a href=\"#CNX_Chem_09_01_Pressure2\" class=\"autogenerated-content\">Figure 2<\/a>\u2014the elephant or the figure skater? A large African elephant can weigh 7 tons, supported on four feet, each with a diameter of about 1.5 ft (footprint area of 250 in<sup>2<\/sup>), so the pressure exerted by each foot is about 14 lb\/in<sup>2<\/sup>:<\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idm100445488\" style=\"text-align: center\">$latex \\text{pressure per elephant foot} = 14,000 \\frac{\\text{lb}}{\\text{elephant}} \\times \\frac{1 \\;\\text{elephant}}{4 \\;\\text{feet}} \\times \\frac{1 \\;\\text{foot}}{250 \\;\\text{in}^2} = 14 \\;\\text{lb\/in}^2$<\/div>\r\n<p id=\"fs-idp79686656\">The figure skater weighs about 120 lbs, supported on two skate blades, each with an area of about 2 in<sup>2<\/sup>, so the pressure exerted by each blade is about 30 lb\/in<sup>2<\/sup>:<\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idm181738992\" style=\"text-align: center\">$latex \\text{pressure per skate blade} = 120 \\frac{\\text{lb}}{\\text{skater}} \\times \\frac{1 \\;\\text{skater}}{2 \\;\\text{blades}} \\times \\frac{1 \\;\\text{blade}}{2 \\;\\text{in}^2} = 30 \\;\\text{lb\/in}^2$<\/div>\r\n<p id=\"fs-idm101012528\">Even though the elephant is more than one hundred-times heavier than the skater, it exerts less than one-half of the pressure and would therefore be less likely to fall though thin ice. On the other hand, if the skater removes her skates and stands with bare feet (or regular footwear) on the ice, the larger area over which her weight is applied greatly reduces the pressure exerted:<\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idp9821216\" style=\"text-align: center\">$latex \\text{pressure per human foot} = 120 \\frac{\\text{lb}}{\\text{skater}} \\times \\frac{1 \\;\\text{skater}}{2 \\;\\text{feet}} \\times \\frac{1 \\;\\text{foot}}{30 \\;\\text{in}^2} = 2 \\;\\text{lb\/in}^2$<\/div>\r\n<figure id=\"CNX_Chem_09_01_Pressure2\"><figcaption>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"975\"]<a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Pressure2.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Pressure2.jpg\" alt=\"This figure includes two photographs. Figure a is a photo of a large gray elephant on grassy, beige terrain. Figure b is a photo of a figure skater with her right skate on the ice, upper torso lowered, arms extended upward behind her chest, and left leg extended upward behind her.\" width=\"975\" height=\"376\" \/><\/a> <strong>Figure 2.<\/strong> Although (a) an elephant\u2019s weight is large, creating a very large force on the ground, (b) the figure skater exerts a much higher pressure on the ice due to the small surface area of her skates. (credit a: modification of work by Guido da Rozze; credit b: modification of work by Ryosuke Yagi)[\/caption]\r\n\r\n<\/figcaption><\/figure>\r\nThe SI unit of pressure is the <strong>pascal (Pa)<\/strong>, with 1 Pa = 1 N\/m<sup>2<\/sup>, where N is the newton, a unit of force defined as 1 kg m\/s<sup>2<\/sup>. One pascal is a small pressure; in many cases, it is more convenient to use units of kilopascal (1 kPa = 1000 Pa) or <strong>bar<\/strong> (1 bar = 100,000 Pa). In the United States, pressure is often measured in pounds of force on an area of one square inch\u2014<strong>pounds per square inch (psi)<\/strong>\u2014for example, in car tires. Pressure can also be measured using the unit <strong>atmosphere (atm)<\/strong>, which originally represented the average sea level air pressure at the approximate latitude of Paris (45\u00b0). <a href=\"#fs-idp189967312\" class=\"autogenerated-content\">Table 1<\/a> provides some information on these and a few other common units for pressure measurements\r\n<table id=\"fs-idp189967312\" class=\"span-all\" summary=\"This table has two columns and 10 rows. The first row is a header row, and it labels the columns as \u201cUnit Name and Abbreviation\u201d and \u201cDefinition or Relation to Other Unit.\u201d The first unit name and abbreviation is pascal, and it is abbreviated as P a. The definition or relation to other unit is 1 P a equals N over m squared and recommended I U P A C unit. The next unit name is kilopascal, and it is abbreviated as k P a. The definition or relation to other unit is 1 k P a equals 1000 P a. The next unit name is pounds per square inch, and it is abbreviated as p s i. The definition or relation to other unit is air pressure at sea level is approximately 14.7 p s i. The next unit name is atmosphere, and is is abbreviated as a t m. The definition or relation to other unit is 1 a t m equals 101,325 P a and air pressure at sea level is approximately one a t m. The next unit name is bar, and it is abbreviated as bar or b. The definition or relation to other unit is 1 bar equals 100,000 P a exactly and commonly used in meteorology. The next unit name is millibar, and it is abbreviated as m b a r or m b. The definition or relation to other unit is 1000 m b a r equals one bar. The next unit name is inches of mercury, and it is abbreviated as i n period, H g. The definition or relation to other unit is one i n period H g equals 3386 P a and is used by the aviation industry and also some weather reports. The next unit is torr. The definition or relation to other unit is 1 torr equals 1 over 760 a t m and named after Evangelista Torricelli, inventor of the barometer. The last unit name is millimeters of mercury, and it is abbreviated as m m H g. The definition or relation to other unit is 1 m m H g is approximately 1 torr.\">\r\n<thead>\r\n<tr valign=\"top\">\r\n<th>Unit Name and Abbreviation<\/th>\r\n<th>Definition or Relation to Other Unit<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td>pascal (Pa)<\/td>\r\n<td>1 Pa = 1 N\/m<sup>2<\/sup>\r\n<div><\/div>\r\nrecommended IUPAC unit<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>kilopascal (kPa)<\/td>\r\n<td>1 kPa = 1000 Pa<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>pounds per square inch (psi)<\/td>\r\n<td>air pressure at sea level is ~14.7 psi<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>atmosphere (atm)<\/td>\r\n<td>1 atm = 101,325 Pa\r\n<div><\/div>\r\nair pressure at sea level is ~1 atm<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>bar (bar, or b)<\/td>\r\n<td>1 bar = 100,000 Pa (exactly)\r\n<div><\/div>\r\ncommonly used in meteorology<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>millibar (mbar, or mb)<\/td>\r\n<td>1000 mbar = 1 bar<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>inches of mercury (in. Hg)<\/td>\r\n<td>1 in. Hg = 3386 Pa\r\n<div><\/div>\r\nused by aviation industry, also some weather reports<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>torr<\/td>\r\n<td>$latex 1 \\;\\text{torr} = \\frac{1}{760} \\;\\text{atm}$\r\n<div><\/div>\r\nnamed after Evangelista Torricelli, inventor of the barometer<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>millimeters of mercury (mm Hg)<\/td>\r\n<td>1 mm Hg ~1 torr<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td colspan=\"2\"><strong>Table 1.<\/strong>\u00a0Pressure Units<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<div class=\"textbox shaded\" id=\"fs-idp156787120\">\r\n<h3>Example 1<\/h3>\r\n<p id=\"fs-idm55125200\"><strong>Conversion of Pressure Units<\/strong>\r\nThe United States National Weather Service reports pressure in both inches of Hg and millibars. Convert a pressure of 29.2 in. Hg into:<\/p>\r\n<p id=\"fs-idp142663424\">(a) torr<\/p>\r\n<p id=\"fs-idp6847648\">(b) atm<\/p>\r\n<p id=\"fs-idm78213376\">(c) kPa<\/p>\r\n<p id=\"fs-idp62713296\">(d) mbar<\/p>\r\n<p id=\"fs-idp32588880\"><strong>Solution<\/strong>\r\nThis is a unit conversion problem. The relationships between the various pressure units are given in <a href=\"#fs-idp189967312\" class=\"autogenerated-content\">Table 1<\/a>.<\/p>\r\n<p id=\"fs-idm19510112\">(a) $latex 29.2 \\;\\rule[0.5ex]{2.2em}{0.1ex}\\hspace{-2.2em}\\text{in Hg} \\times \\frac{25.4 \\;\\rule[0.25ex]{1.2em}{0.1ex}\\hspace{-1.2em}\\text{mm}}{1 \\;\\rule[0.25ex]{0.6em}{0.1ex}\\hspace{-0.6em}\\text{in}} \\times \\frac{1 \\;\\text{torr}}{1 \\;\\rule[0.25ex]{2em}{0.1ex}\\hspace{-2em}\\text{mm Hg}} = 742 \\;\\text{torr}$<\/p>\r\n<p id=\"fs-idm103224224\">(b) $latex 742 \\;\\rule[0.5ex]{1.8em}{0.1ex}\\hspace{-1.8em}\\text{torr} \\times \\frac{1 \\;\\text{atm}}{760 \\;\\rule[0.25ex]{1.2em}{0.1ex}\\hspace{-1.2em}\\text{torr}} = 0.976 \\;\\text{atm}$<\/p>\r\n<p id=\"fs-idp28156048\">(c) $latex 742 \\;\\rule[0.5ex]{1.8em}{0.1ex}\\hspace{-1.8em}\\text{torr} \\times \\frac{101.325 \\;\\text{kPa}}{760 \\;\\rule[0.25ex]{1.0em}{0.1ex}\\hspace{-1.0em}\\text{torr}} = 98.9 \\;\\text{kPa}$<\/p>\r\n<p id=\"fs-idm86928016\">(d) $latex 98.9 \\;\\rule[0.5ex]{1.9em}{0.1ex}\\hspace{-1.9em}\\text{kPa} \\times \\frac{1000 \\;\\rule[0.25ex]{0.9em}{0.1ex}\\hspace{-0.9em}\\text{Pa}}{1 \\;\\rule[0.25ex]{1.1em}{0.1ex}\\hspace{-1.1em}\\text{kPa}} \\times \\frac{1 \\;\\rule[0.25ex]{0.9em}{0.1ex}\\hspace{-0.9em}\\text{bar}}{100,000 \\;\\rule[0.25ex]{1.0em}{0.1ex}\\hspace{-1.0em}\\text{Pa}} \\times \\frac{1000 \\;\\text{mbar}}{1 \\;\\rule[0.25ex]{1.0em}{0.1ex}\\hspace{-1.0em}\\text{bar}} = 989 \\;\\text{mbar}$<\/p>\r\n<p id=\"fs-idm28185008\"><strong>Check Your Learning<\/strong>\r\nA typical barometric pressure in Kansas City is 740 torr. What is this pressure in atmospheres, in millimeters of mercury, in kilopascals, and in bar?<\/p>\r\n\r\n<div class=\"textbox shaded\" id=\"fs-idm54955856\">\r\n<h3 class=\"title\">Answer:<\/h3>\r\n<p id=\"fs-idp131216672\">0.974 atm; 740 mm Hg; 98.7 kPa; 0.987 bar<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<p id=\"fs-idm69336128\">We can measure atmospheric pressure, the force exerted by the atmosphere on the earth\u2019s surface, with a <strong>barometer<\/strong> (<a href=\"#CNX_Chem_09_01_Barometer\" class=\"autogenerated-content\">Figure 3<\/a>). A barometer is a glass tube that is closed at one end, filled with a nonvolatile liquid such as mercury, and then inverted and immersed in a container of that liquid. The atmosphere exerts pressure on the liquid outside the tube, the column of liquid exerts pressure inside the tube, and the pressure at the liquid surface is the same inside and outside the tube. The height of the liquid in the tube is therefore proportional to the pressure exerted by the atmosphere.<\/p>\r\n\r\n<figure id=\"CNX_Chem_09_01_Barometer\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"650\"]<a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Barometer.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Barometer.jpg\" alt=\"This figure shows two barometers. The barometer to the left contains a shallow reservoir, or open container, of mercury. A narrow tube extends upward from the reservoir above the reservoir. This tube is sealed at the top. To the right, a second similar setup is shown with a reservoir filled with water. Line segments connect the label \u201cvacuum\u201d to the tops of the two narrow tubes. The tube on the left shows the mercury in the reservoir extending in a column upward in the narrow tube. Similarly, the tube on the right shows the water in the reservoir extending upward into the related narrow tube. Double-headed arrows extend from the surface of each liquid in the reservoir to the top of the liquid in each tube. A narrow column or bar extends from the surface of the reservoir to the same height. This bar is labeled \u201catmospheric pressure.\u201d The level of the water in its tube is significantly higher than the level of mercury in its tube.\" width=\"650\" height=\"647\" \/><\/a> <strong>Figure 3.<\/strong> In a barometer, the height, <em>h<\/em>, of the column of liquid is used as a measurement of the air pressure. Using very dense liquid mercury (left) permits the construction of reasonably sized barometers, whereas using water (right) would require a barometer more than 30 feet tall.[\/caption]<\/figure>\r\n<p id=\"fs-idm79676464\">If the liquid is water, normal atmospheric pressure will support a column of water over 10 meters high, which is rather inconvenient for making (and reading) a barometer. Because mercury (Hg) is about 13.6-times denser than water, a mercury barometer only needs to be $latex \\frac{1}{13.6}$ as tall as a water barometer\u2014a more suitable size. Standard atmospheric pressure of 1 atm at sea level (101,325 Pa) corresponds to a column of mercury that is about 760 mm (29.92 in.) high. The <strong>torr<\/strong> was originally intended to be a unit equal to one millimeter of mercury, but it no longer corresponds exactly. The pressure exerted by a fluid due to gravity is known as <strong>hydrostatic pressure<\/strong>, <em>p<\/em>:<\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idm35258720\" style=\"text-align: center\">$latex p = h\\rho g$<\/div>\r\n<p id=\"fs-idm61000288\">where <em>h<\/em> is the height of the fluid, <em>\u03c1<\/em> is the density of the fluid, and <em>g<\/em> is acceleration due to gravity.<\/p>\r\n\r\n<div class=\"textbox shaded\" id=\"fs-idm5509408\">\r\n<h3>Example 2<\/h3>\r\n<p id=\"fs-idm124424064\"><strong>Calculation of Barometric Pressure<\/strong>\r\nShow the calculation supporting the claim that atmospheric pressure near sea level corresponds to the pressure exerted by a column of mercury that is about 760 mm high. The density of mercury = 13.6 g\/cm<sup>3<\/sup>.<\/p>\r\n<p id=\"fs-idm64631536\"><strong>Solution<\/strong>\r\nThe hydrostatic pressure is given by <em>p<\/em> = <em>h\u03c1g<\/em>, with <em>h<\/em> = 760 mm, <em>\u03c1<\/em> = 13.6 g\/cm<sup>3<\/sup>, and <em>g<\/em> = 9.81 m\/s<sup>2<\/sup>. Plugging these values into the equation and doing the necessary unit conversions will give us the value we seek. (Note: We are expecting to find a pressure of ~101,325 Pa:)<\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idm207611040\" style=\"text-align: center\">$latex 101,325 N\/ \\text{m}^2 = 101,325 \\frac{\\text{kg} \\cdot \\text{m\/s}^2}{\\text{m}^2} = 101,325 \\frac{\\text{kg}}{\\text{m} \\cdot \\text{s}^2}$<\/div>\r\n<div class=\"equation\" id=\"fs-idm149736288\" style=\"text-align: center\">$latex \\begin{array}{l @{{}={}}l} p &amp; (760 \\;\\text{mm} \\times \\frac{1 \\;\\text{m}}{1000 \\;\\text{mm}}) \\times (\\frac{13.6 \\;\\text{g}}{1 \\;\\text{cm}^3} \\times \\frac{1 \\;\\text{kg}}{1000 \\;\\text{g}} \\times \\frac{(100 \\;\\text{cm})^3}{(1 \\;\\text{m})^3}) \\times (\\frac{9.81 \\;\\text{m}}{1 \\;\\text{s}^2}) \\\\[1em] &amp; (0.760 \\;\\text{m}) (13,600 \\;\\text{kg\/m}^3) (9.81 \\;\\text{m\/s}^2) = 1.01 \\times 10^5 \\;\\text{kg\/ms}^2 = 1.01 \\times 10^5 \\;N\/ \\text{m}^2 \\\\[1em] &amp; 1.01 \\times 10^5 \\;\\text{Pa} \\end{array}$<\/div>\r\n<p id=\"fs-idp70400640\"><strong>Check Your Learning<\/strong>\r\nCalculate the height of a column of water at 25 \u00b0C that corresponds to normal atmospheric pressure. The density of water at this temperature is 1.0 g\/cm<sup>3<\/sup>.<\/p>\r\n\r\n<div class=\"textbox shaded\" id=\"fs-idp73341600\">\r\n<h3 class=\"title\">Answer:<\/h3>\r\n<p id=\"fs-idp2146864\">10.3 m<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<p id=\"fs-idp189718992\">A <strong>manometer<\/strong> is a device similar to a barometer that can be used to measure the pressure of a gas trapped in a container. A closed-end manometer is a U-shaped tube with one closed arm, one arm that connects to the gas to be measured, and a nonvolatile liquid (usually mercury) in between. As with a barometer, the distance between the liquid levels in the two arms of the tube (<em>h<\/em> in the diagram) is proportional to the pressure of the gas in the container. An open-end manometer (<a href=\"#CNX_Chem_09_01_Manometer\" class=\"autogenerated-content\">Figure 4<\/a>) is the same as a closed-end manometer, but one of its arms is open to the atmosphere. In this case, the distance between the liquid levels corresponds to the difference in pressure between the gas in the container and the atmosphere.<\/p>\r\n\r\n<figure id=\"CNX_Chem_09_01_Manometer\"><figcaption>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1300\"]<a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Manometer.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer.jpg\" alt=\"Three diagrams of manometers are shown. Each manometer consists of a spherical pink container filled with gas on the left that is connected to a U-shaped, sealed tube by a valve on its right. The top of the U-shape aligns with the gas-filled sphere and the U, which extends below, contains mercury. The first manometer has a sealed tube. The sealed end to the upper right in the diagram is labeled \u201cclosed end\u201d and \u201cvacuum.\u201d An arrow points downward in the left side of the U shaped tube to the mercury surface. This arrow is labeled \u201cP subscript gas.\u201d The mercury level is higher in the right side of the tube than in the left. The difference in height is labeled \u201ch.\u201d Beneath this manometer illustration appears the label P subscript gas equal sign h rho g. The second manometer has an open ended tube, which is labeled \u201copen end.\u201d At this opening in the upper right of the diagram is a downward arrow, above which is the label P subscript a t m. An arrow points downward in the left side of the U shaped tube to the mercury surface. This arrow is labeled \u201cP subscript gas.\u201d The mercury level is higher in the left side of the tube than in the right. This difference in height is labeled \u201ch.\u201d Beneath this manometer illustration appears the label P subscript gas equal sign P subscript a t m minus sign h rho g. The third manometer has an open ended tube and is similar to the second manometer except that mercury level is higher in the right side of the tube than in the left. This difference in height is labeled \u201ch.\u201d Beneath this manometer illustration appears the label P subscript gas equal sign P subscript a t m plus h rho g.\" width=\"1300\" height=\"456\" \/><\/a> <strong>Figure 4.<\/strong> A manometer can be used to measure the pressure of a gas. The (difference in) height between the liquid levels (<em>h<\/em>) is a measure of the pressure. Mercury is usually used because of its large density.[\/caption]\r\n\r\n<\/figcaption><\/figure>\r\n<div class=\"textbox shaded\" id=\"fs-idm31201088\">\r\n<h3>Example 3<\/h3>\r\n<p id=\"fs-idp5332928\"><strong>Calculation of Pressure Using a Closed-End Manometer<\/strong>\r\nThe pressure of a sample of gas is measured with a closed-end manometer, as shown to the right. The liquid in the manometer is mercury. Determine the pressure of the gas in:<\/p>\r\n<p id=\"fs-idp161989312\">(a) torr<\/p>\r\n<p id=\"fs-idp16104736\">(b) Pa<\/p>\r\n<p id=\"fs-idm85992448\">(c) bar<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer1_img.jpg\" alt=\"A diagram of a closed-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201cclosed end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height between the left side and right side is 26.4 c m which is indicated with horizontal line segments and arrows.\" \/>\r\n<p id=\"fs-idm79648128\"><strong>Solution<\/strong>\r\nThe pressure of the gas is equal to a column of mercury of height 26.4 cm. (The pressure at the bottom horizontal line is equal on both sides of the tube. The pressure on the left is due to the gas and the pressure on the right is due to 26.4 cm Hg, or mercury.) We could use the equation <em>p<\/em> = <em>h\u03c1g<\/em> as in <a href=\"#fs-idm5509408\" class=\"autogenerated-content\">Example 2<\/a>, but it is simpler to just convert between units using <a href=\"#fs-idp189967312\" class=\"autogenerated-content\">Table 1<\/a>.<\/p>\r\n<p id=\"fs-idm79108064\">(a) $latex 26.4 \\;\\rule[0.5ex]{2.8em}{0.1ex}\\hspace{-2.8em}\\text{cm Hg} \\times \\frac{10 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}}{1 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}} \\times \\frac{1 \\;\\text{torr}}{1 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}} = 264 \\;\\text{torr}$<\/p>\r\n<p id=\"fs-idp62655904\">(b) $latex 264 \\;\\rule[0.5ex]{1.7em}{0.1ex}\\hspace{-1.7em}\\text{torr} \\times \\frac{1 \\;\\rule[0.25ex]{1.3em}{0.1ex}\\hspace{-1.3em}\\text{atm}}{760 \\;\\rule[0.25ex]{1.3em}{0.1ex}\\hspace{-1.3em}\\text{torr}} \\times \\frac{101,325 \\;\\text{Pa}}{1 \\;\\rule[0.25ex]{1.3em}{0.1ex}\\hspace{-1,3em}\\text{atm}} = 35,200 \\;\\text{Pa}$<\/p>\r\n<p id=\"fs-idp2045200\">(c) $latex 35,200 \\;\\rule[0.5ex]{1.2em}{0.1ex}\\hspace{-1.2em}\\text{Pa} \\times \\frac{1 \\;\\text{bar}}{100,000 \\;\\rule[0.25ex]{1em}{0.1ex}\\hspace{-1em}\\text{Pa}} = 0.352 \\;\\text{bar}$<\/p>\r\n<p id=\"fs-idp37894320\"><strong>Check Your Learning<\/strong>\r\nThe pressure of a sample of gas is measured with a closed-end manometer. The liquid in the manometer is mercury. Determine the pressure of the gas in:<\/p>\r\n<p id=\"fs-idp38024128\">(a) torr<\/p>\r\n<p id=\"fs-idp16117232\">(b) Pa<\/p>\r\n<p id=\"fs-idp127919232\">(c) bar<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer2_img.jpg\" alt=\"A diagram of a closed-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201cclosed end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 6.0 i n is indicated with horizontal line segments and arrows.\" \/>\r\n<div class=\"textbox shaded\" id=\"fs-idm70430576\">\r\n<h3 class=\"title\">Answer:<\/h3>\r\n<p id=\"fs-idm8669760\">(a) ~150 torr; (b) ~20,000 Pa; (c) ~0.20 bar<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\" id=\"fs-idm76587328\">\r\n<h3>Example\u00a04<\/h3>\r\n<p id=\"fs-idm12992864\"><strong>Calculation of Pressure Using an Open-End Manometer<\/strong>\r\nThe pressure of a sample of gas is measured at sea level with an open-end Hg (mercury) manometer, as shown to the right. Determine the pressure of the gas in:<\/p>\r\n<p id=\"fs-idp141807120\">(a) mm Hg<\/p>\r\n<p id=\"fs-idm91216192\">(b) atm<\/p>\r\n<p id=\"fs-idm29337808\">(c) kPa<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer3_img.jpg\" alt=\"A diagram of an opne-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 13.7 c m is indicated with horizontal line segments and arrows.\" \/>\r\n<p id=\"fs-idp6251232\"><strong>Solution<\/strong>\r\nThe pressure of the gas equals the hydrostatic pressure due to a column of mercury of height 13.7 cm plus the pressure of the atmosphere at sea level. (The pressure at the bottom horizontal line is equal on both sides of the tube. The pressure on the left is due to the gas and the pressure on the right is due to 13.7 cm of Hg plus atmospheric pressure.)<\/p>\r\n<p id=\"fs-idp139076928\">(a) In mm Hg, this is: 137 mm Hg + 760 mm Hg = 897 mm Hg<\/p>\r\n<p id=\"fs-idm20839232\">(b) $latex 897 \\;\\rule[0.5ex]{3em}{0.1ex}\\hspace{-3em}\\text{mm Hg} \\times \\frac{1 \\;\\text{atm}}{760 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}} = 1.18 \\;\\text{atm}$<\/p>\r\n<p id=\"fs-idp8049056\">(c) $latex 1.18 \\;\\rule[0.5ex]{1.8em}{0.1ex}\\hspace{-1.8em}\\text{atm} \\times \\frac{101.325 \\;\\text{kPa}}{1 \\;\\rule[0.25ex]{1.5em}{0.1ex}\\hspace{-1.5em}\\text{atm}} = 1.20 \\times 10^2 \\;\\text{kPa}$<\/p>\r\n<p id=\"fs-idm24876576\"><strong>Check Your Learning<\/strong>\r\nThe pressure of a sample of gas is measured at sea level with an open-end Hg manometer, as shown to the right. Determine the pressure of the gas in:<\/p>\r\n<p id=\"fs-idp30718048\">(a) mm Hg<\/p>\r\n<p id=\"fs-idm5192960\">(b) atm<\/p>\r\n<p id=\"fs-idp18503824\">(c) kPa<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_manometer4_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the left side than on the right. The difference in height of 4.63 i n is indicated with horizontal line segments and arrows.\" \/>\r\n<div class=\"textbox shaded\" id=\"fs-idp173017200\">\r\n<h3 class=\"title\">Answer:<\/h3>\r\n<p id=\"fs-idp154771664\">(a) 642 mm Hg; (b) 0.845 atm; (c) 85.6 kPa<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp183412160\" class=\"textbox shaded\">\r\n<h3 class=\"title\">Measuring Blood Pressure<\/h3>\r\n<p id=\"fs-idm61054480\">Blood pressure is measured using a device called a sphygmomanometer (Greek <em>sphygmos<\/em> = \u201cpulse\u201d). It consists of an inflatable cuff to restrict blood flow, a manometer to measure the pressure, and a method of determining when blood flow begins and when it becomes impeded (<a href=\"#CNX_Chem_09_01_Spygmo\" class=\"autogenerated-content\">Figure 5<\/a>). Since its invention in 1881, it has been an essential medical device. There are many types of sphygmomanometers: manual ones that require a stethoscope and are used by medical professionals; mercury ones, used when the most accuracy is required; less accurate mechanical ones; and digital ones that can be used with little training but that have limitations. When using a sphygmomanometer, the cuff is placed around the upper arm and inflated until blood flow is completely blocked, then slowly released. As the heart beats, blood forced through the arteries causes a rise in pressure. This rise in pressure at which blood flow begins is the <em>systolic pressure\u2014<\/em>the peak pressure in the cardiac cycle. When the cuff\u2019s pressure equals the arterial systolic pressure, blood flows past the cuff, creating audible sounds that can be heard using a stethoscope. This is followed by a decrease in pressure as the heart\u2019s ventricles prepare for another beat. As cuff pressure continues to decrease, eventually sound is no longer heard; this is the <em>diastolic pressure\u2014<\/em>the lowest pressure (resting phase) in the cardiac cycle. Blood pressure units from a sphygmomanometer are in terms of millimeters of mercury (mm Hg).<\/p>\r\n\r\n<figure id=\"CNX_Chem_09_01_Spygmo\"><figcaption>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"975\"]<a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Spygmo.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Spygmo.jpg\" alt=\"This figure includes two photographs. The first photo shows a young adult male placing a blood pressure cuff on the upper arm of a young adult female. The second image shows a typical sphygmomanometer, which includes a black blood pressure cuff, tubing, pump, and pressure gauge.\" width=\"975\" height=\"313\" \/><\/a> <strong>Figure 5.<\/strong> (a) A medical technician prepares to measure a patient\u2019s blood pressure with a sphygmomanometer. (b) A typical sphygmomanometer uses a valved rubber bulb to inflate the cuff and a diaphragm gauge to measure pressure. (credit a: modification of work by Master Sgt. Jeffrey Allen)[\/caption]\r\n\r\n<\/figcaption><\/figure>\r\n<\/div>\r\n<div id=\"fs-idm96003696\" class=\"textbox shaded\">\r\n<h3 class=\"title\">Meteorology, Climatology, and Atmospheric Science<\/h3>\r\n<p id=\"fs-idm77491200\">Throughout the ages, people have observed clouds, winds, and precipitation, trying to discern patterns and make predictions: when it is best to plant and harvest; whether it is safe to set out on a sea voyage; and much more. We now face complex weather and atmosphere-related challenges that will have a major impact on our civilization and the ecosystem. Several different scientific disciplines use chemical principles to help us better understand weather, the atmosphere, and climate. These are meteorology, climatology, and atmospheric science. Meteorology is the study of the atmosphere, atmospheric phenomena, and atmospheric effects on earth\u2019s weather. Meteorologists seek to understand and predict the weather in the short term, which can save lives and benefit the economy. Weather forecasts (<a href=\"#CNX_Chem_09_01_WeatherMap\" class=\"autogenerated-content\">Figure 6<\/a>) are the result of thousands of measurements of air pressure, temperature, and the like, which are compiled, modeled, and analyzed in weather centers worldwide.<\/p>\r\n\r\n<figure id=\"CNX_Chem_09_01_WeatherMap\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"650\"]<a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_WeatherMap.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_WeatherMap.jpg\" alt=\"A weather map of the United States is shown which points out areas of high and low pressure with the letters H in blue and L in red. Curved lines in grey, orange, blue, and red are shown. The orange lines are segmented. The red and blue lines have small red or blue semi-circles and triangles attached along their lengths. In dashed white lines, latitude and longitude are indicated. Underlined three and four digit numbers also appear across the map.\" width=\"650\" height=\"402\" \/><\/a> <strong>Figure 6.<\/strong> Meteorologists use weather maps to describe and predict weather. Regions of high (H) and low (L) pressure have large effects on weather conditions. The gray lines represent locations of constant pressure known as isobars. (credit: modification of work by National Oceanic and Atmospheric Administration)[\/caption]<\/figure>\r\n<p id=\"fs-idm8048304\">In terms of weather, low-pressure systems occur when the earth\u2019s surface atmospheric pressure is lower than the surrounding environment: Moist air rises and condenses, producing clouds. Movement of moisture and air within various weather fronts instigates most weather events.<\/p>\r\n<p id=\"fs-idm49021728\">The atmosphere is the gaseous layer that surrounds a planet. Earth\u2019s atmosphere, which is roughly 100\u2013125 km thick, consists of roughly 78.1% nitrogen and 21.0% oxygen, and can be subdivided further into the regions shown in <a href=\"#CNX_Chem_09_01_Atmosphere\" class=\"autogenerated-content\">Figure 7<\/a>: the exosphere (furthest from earth, &gt; 700 km above sea level), the thermosphere (80\u2013700 km), the mesosphere (50\u201380 km), the stratosphere (second lowest level of our atmosphere, 12\u201350 km above sea level), and the troposphere (up to 12 km above sea level, roughly 80% of the earth\u2019s atmosphere by mass and the layer where most weather events originate). As you go higher in the troposphere, air density and temperature both decrease.<\/p>\r\n\r\n<figure id=\"CNX_Chem_09_01_Atmosphere\"><figcaption>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1200\"]<a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Atmosphere.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Atmosphere.jpg\" alt=\"This diagram shows half of a two dimensional view of the earth in blue and green. A narrow white layer, labeled \u201ctroposphere 0 dash 12 k m\u201d covers this hemisphere. This layer is also labeled \u201clayer where most weather events originate.\u201d Next, a thicker light blue layer labeled \u201cStratosphere 12 dash 50 k m\u201d is shown. This is followed by a slightly thinner layer also in light blue labeled \u201cMesosphere 50 dash 80 k m.\u201d Following this layer is a relatively thick light blue layer labeled \u201cThermosphere 80 dash 700 k m.\u201d A blue layer appears that covers the rightmost two thirds of the diagram. This region gradually darkens from a lighter blue at the left to a dark blue at the right. This region of the diagram is labeled \u201cexosphere greater than 700 k m.\u201d\" width=\"1200\" height=\"547\" \/><\/a> <strong> Figure 7.<\/strong> Earth\u2019s atmosphere has five layers: the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.[\/caption]\r\n\r\n<\/figcaption><\/figure>\r\n<p id=\"fs-idm30549520\">Climatology is the study of the climate, averaged weather conditions over long time periods, using atmospheric data. However, climatologists study patterns and effects that occur over decades, centuries, and millennia, rather than shorter time frames of hours, days, and weeks like meteorologists. Atmospheric science is an even broader field, combining meteorology, climatology, and other scientific disciplines that study the atmosphere.<\/p>\r\n\r\n<\/div>\r\n<section id=\"fs-idm62097440\" class=\"summary\">\r\n<h1>Key Concepts and Summary<\/h1>\r\n<p id=\"fs-idm102779232\">Gases exert pressure, which is force per unit area. The pressure of a gas may be expressed in the SI unit of pascal or kilopascal, as well as in many other units including torr, atmosphere, and bar. Atmospheric pressure is measured using a barometer; other gas pressures can be measured using one of several types of manometers.<\/p>\r\n\r\n<\/section><section id=\"fs-idp68662112\" class=\"key-equations\">\r\n<h1>Key Equations<\/h1>\r\n<ul id=\"fs-idm103206560\">\r\n \t<li>$latex P = \\frac{F}{A}$<\/li>\r\n \t<li>$latex p = h \\rho g$<\/li>\r\n<\/ul>\r\n<\/section><section id=\"fs-idm20163680\" class=\"exercises\">\r\n<div class=\"bcc-box bcc-info\">\r\n<h3 itemprop=\"educationalUse\">Chemistry End of Chapter Exercises<\/h3>\r\n<ol>\r\n \t<li id=\"fs-idm19553744\">Why are sharp knives more effective than dull knives (Hint: think about the definition of pressure)?<\/li>\r\n \t<li id=\"fs-idp62697024\">Why do some small bridges have weight limits that depend on how many wheels or axles the crossing vehicle has?<\/li>\r\n \t<li id=\"fs-idm50132240\">Why should you roll or belly-crawl rather than walk across a thinly-frozen pond?<\/li>\r\n \t<li id=\"fs-idm137597392\">A typical barometric pressure in Redding, California, is about 750 mm Hg. Calculate this pressure in atm and kPa.<\/li>\r\n \t<li id=\"fs-idp3670784\">A typical barometric pressure in Denver, Colorado, is 615 mm Hg. What is this pressure in atmospheres and kilopascals?<\/li>\r\n \t<li id=\"fs-idp135739664\">A typical barometric pressure in Kansas City is 740 torr. What is this pressure in atmospheres, in millimeters of mercury, and in kilopascals?<\/li>\r\n \t<li id=\"fs-idp38342496\">Canadian tire pressure gauges are marked in units of kilopascals. What reading on such a gauge corresponds to 32 psi?<\/li>\r\n \t<li id=\"fs-idm38508352\">During the Viking landings on Mars, the atmospheric pressure was determined to be on the average about 6.50 millibars (1 bar = 0.987 atm). What is that pressure in torr and kPa?<\/li>\r\n \t<li id=\"fs-idm88643488\">The pressure of the atmosphere on the surface of the planet Venus is about 88.8 atm. Compare that pressure in psi to the normal pressure on earth at sea level in psi.<\/li>\r\n \t<li id=\"fs-idm38299280\">A medical laboratory catalog describes the pressure in a cylinder of a gas as 14.82 MPa. What is the pressure of this gas in atmospheres and torr?<\/li>\r\n \t<li id=\"fs-idp39879760\">Consider this scenario and answer the following questions: On a mid-August day in the northeastern United States, the following information appeared in the local newspaper: atmospheric pressure at sea level 29.97 in., 1013.9 mbar.\r\n<p id=\"fs-idm50271520\">(a) What was the pressure in kPa?<\/p>\r\n<p id=\"fs-idp189723312\">(b) The pressure near the seacoast in the northeastern United States is usually reported near 30.0 in. Hg. During a hurricane, the pressure may fall to near 28.0 in. Hg. Calculate the drop in pressure in torr.<\/p>\r\n<\/li>\r\n \t<li id=\"fs-idp26220160\">Why is it necessary to use a nonvolatile liquid in a barometer or manometer?<\/li>\r\n \t<li id=\"fs-idm29763808\">The pressure of a sample of gas is measured at sea level with a closed-end manometer. The liquid in the manometer is mercury. Determine the pressure of the gas in:\r\n<p id=\"fs-idp89607040\">(a) torr<\/p>\r\n<p id=\"fs-idm95742832\">(b) Pa<\/p>\r\n<p id=\"fs-idm80328752\">(c) bar<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer5_img.jpg\" alt=\"A diagram of a closed-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201cclosed end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 26.4 c m is indicated with horizontal line segments and arrows.\" \/><\/li>\r\n \t<li id=\"fs-idp185367488\">The pressure of a sample of gas is measured with an open-end manometer, partially shown to the right. The liquid in the manometer is mercury. Assuming atmospheric pressure is 29.92 in. Hg, determine the pressure of the gas in:\r\n<p id=\"fs-idm39627648\">(a) torr<\/p>\r\n<p id=\"fs-idp27090112\">(b) Pa<\/p>\r\n<p id=\"fs-idm69293536\">(c) bar<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer6_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the left side than on the right. The difference in height of 6.00 i n is indicated with horizontal line segments and arrows.\" \/><\/li>\r\n \t<li id=\"fs-idm86041584\">The pressure of a sample of gas is measured at sea level with an open-end mercury manometer. Assuming atmospheric pressure is 760.0 mm Hg, determine the pressure of the gas in:\r\n<p id=\"fs-idp164256000\">(a) mm Hg<\/p>\r\n<p id=\"fs-idp142813824\">(b) atm<\/p>\r\n<p id=\"fs-idp30379328\">(c) kPa<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer7_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the left side than on the right. The difference in height of 13.7 c m is indicated with horizontal line segments and arrows.\" \/><\/li>\r\n \t<li>The pressure of a sample of gas is measured at sea level with an open-end mercury manometer. Assuming atmospheric pressure is 760 mm Hg, determine the pressure of the gas in:\r\n<p id=\"fs-idm77467552\">(a) mm Hg<\/p>\r\n<p id=\"fs-idm90142112\">(b) atm<\/p>\r\n<p id=\"fs-idp189802448\">(c) kPa<\/p>\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer8_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 26.4 c m is indicated with horizontal line segments and arrows.\" \/><\/li>\r\n \t<li id=\"fs-idm79130144\">How would the use of a volatile liquid affect the measurement of a gas using open-ended manometers vs. closed-end manometers?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/section>\r\n<div>\r\n<h2>Glossary<\/h2>\r\n<dl id=\"fs-idm92046304\" class=\"definition\">\r\n \t<dt>atmosphere (atm)<\/dt>\r\n \t<dd id=\"fs-idm48979616\">unit of pressure; 1 atm = 101,325 Pa<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm49164816\" class=\"definition\">\r\n \t<dt>bar<\/dt>\r\n \t<dd id=\"fs-idm19523424\">(bar or b) unit of pressure; 1 bar = 100,000 Pa<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp128557152\" class=\"definition\">\r\n \t<dt>barometer<\/dt>\r\n \t<dd id=\"fs-idp44432976\">device used to measure atmospheric pressure<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp1898224\" class=\"definition\">\r\n \t<dt>hydrostatic pressure<\/dt>\r\n \t<dd id=\"fs-idm78041232\">pressure exerted by a fluid due to gravity<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm30126128\" class=\"definition\">\r\n \t<dt>manometer<\/dt>\r\n \t<dd id=\"fs-idm91258448\">device used to measure the pressure of a gas trapped in a container<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm69533872\" class=\"definition\">\r\n \t<dt>pascal (Pa)<\/dt>\r\n \t<dd id=\"fs-idm53495904\">SI unit of pressure; 1 Pa = 1 N\/m<sup>2<\/sup><\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm87137504\" class=\"definition\">\r\n \t<dt>pounds per square inch (psi)<\/dt>\r\n \t<dd id=\"fs-idm52430016\">unit of pressure common in the US<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm61385376\" class=\"definition\">\r\n \t<dt>pressure<\/dt>\r\n \t<dd id=\"fs-idm64654544\">force exerted per unit area<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm23965520\" class=\"definition\">\r\n \t<dt>torr<\/dt>\r\n \t<dd id=\"fs-idm55637456\">unit of pressure; $latex 1 \\;\\text{torr} = \\frac{1}{760} \\;\\text{atm}$<\/dd>\r\n<\/dl>\r\n<\/div>\r\n<div class=\"bcc-box bcc-info\">\r\n<h3 itemprop=\"educationalUse\">Solutions<\/h3>\r\n<strong>Answers to Chemistry End of Chapter Exercises<\/strong>\r\n<p id=\"fs-idm33698016\">1. The cutting edge of a knife that has been sharpened has a smaller surface area than a dull knife. Since pressure is force per unit area, a sharp knife will exert a higher pressure with the same amount of force and cut through material more effectively.<\/p>\r\n<p id=\"fs-idp69163280\">3. Lying down distributes your weight over a larger surface area, exerting less pressure on the ice compared to standing up. If you exert less pressure, you are less likely to break through thin ice.<\/p>\r\n<p id=\"fs-idm25200320\">5. 0.809 atm; 82.0 kPa<\/p>\r\n<p id=\"fs-idm5145968\">7. 2.2 \u00d7 10<sup>2<\/sup> kPa<\/p>\r\n<p id=\"fs-idp86259712\">9. Earth: 14.7 lb in<sup>\u20132<\/sup>; Venus: 13.1 \u00d7 10<sup>3<\/sup> lb in<sup>\u22122<\/sup><\/p>\r\n<p id=\"fs-idm21108080\">11. (a) 101.5 kPa; (b) 51 torr drop<\/p>\r\n<p id=\"fs-idm83006352\">13. (a) 264 torr; (b) 35,200 Pa; (c) 0.352 bar<\/p>\r\n<p id=\"fs-idm33920592\">15. (a) 623 mm Hg; (b) 0.820 atm; (c) 83.1 kPa<\/p>\r\n<p id=\"fs-idm51906080\">17. With a closed-end manometer, no change would be observed, since the vaporized liquid would contribute equal, opposing pressures in both arms of the manometer tube. However, with an open-ended manometer, a higher pressure reading of the gas would be obtained than expected, since <em>P<\/em><sub>gas<\/sub> = <em>P<\/em><sub>atm<\/sub> + <em>P<\/em><sub>vol liquid<\/sub>.<\/p>\r\n\r\n<\/div>","rendered":"<div class=\"bcc-box bcc-highlight\">\n<h3 itemprop=\"educationalUse\">Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Define the property of pressure<\/li>\n<li>Define and convert among the units of pressure measurements<\/li>\n<li>Describe the operation of common tools for measuring gas pressure<\/li>\n<li>Calculate pressure from manometer data<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idm2965936\">The earth\u2019s atmosphere exerts a pressure, as does any other gas. Although we do not normally notice atmospheric pressure, we are sensitive to pressure changes\u2014for example, when your ears \u201cpop\u201d during take-off and landing while flying, or when you dive underwater. Gas pressure is caused by the force exerted by gas molecules colliding with the surfaces of objects (<a href=\"#CNX_Chem_09_01_Pressure1\" class=\"autogenerated-content\">Figure 1<\/a>). Although the force of each collision is very small, any surface of appreciable area experiences a large number of collisions in a short time, which can result in a high pressure. In fact, normal air pressure is strong enough to crush a metal container when not balanced by equal pressure from inside the container.<\/p>\n<figure id=\"CNX_Chem_09_01_Pressure1\">\n<figure style=\"width: 975px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Pressure1.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Pressure1.jpg\" alt=\"The left side of this figure includes a graphic of the earth with an inverted rectangular prism extending from a point on it. Near the top of the image, the label, \u201csquare inch column of air molecules\u201d is connected to the prism with a line segment. This label is also connected with a line segment to a downward pointing arrow at the right side of the figure. Beneath the arrow is a red circle labeled, \u201catmospheric pressure.\u201d A narrow rectangle with a dashed line border extends from the bottom of the arrow vertically through the circle. Directly beneath this rectangle at the lower edge of the circle is a hand with a thumb appearing to be resting on a tabletop. The thumb is connected with a line segment to the label, \u201c14.7 lbs of pressure on 1 square inch.\u201d The red circle is sitting on top of the thumb.\" width=\"975\" height=\"458\" \/><\/a><figcaption class=\"wp-caption-text\"><strong>Figure 1.<\/strong> The atmosphere above us exerts a large pressure on objects at the surface of the earth, roughly equal to the weight of a bowling ball pressing on an area the size of a human thumbnail.<\/figcaption><\/figure>\n<\/figure>\n<div id=\"fs-idm5657392\" class=\"textbox shaded\">\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/OSC_Interactive_200-15.png\" alt=\"\u00a0\" \/><\/p>\n<p id=\"fs-idp139792368\">A dramatic <a href=\"http:\/\/openstaxcollege.org\/l\/16atmospressur1\">illustration<\/a> of atmospheric pressure is provided in this brief video, which shows a railway tanker car imploding when its internal pressure is decreased.<\/p>\n<p id=\"fs-idm26057840\">A smaller scale <a href=\"http:\/\/openstaxcollege.org\/l\/16atmospressur2\">demonstration<\/a> of this phenomenon is briefly explained.<\/p>\n<\/div>\n<p id=\"fs-idm5227120\">Atmospheric pressure is caused by the weight of the column of air molecules in the atmosphere above an object, such as the tanker car. At sea level, this pressure is roughly the same as that exerted by a full-grown African elephant standing on a doormat, or a typical bowling ball resting on your thumbnail. These may seem like huge amounts, and they are, but life on earth has evolved under such atmospheric pressure. If you actually perch a bowling ball on your thumbnail, the pressure experienced is<em> twice<\/em> the usual pressure, and the sensation is unpleasant.<\/p>\n<p id=\"fs-idp26888784\">In general, <strong>pressure<\/strong> is defined as the force exerted on a given area: [latex]P = \\frac{F}{A}[\/latex]. Note that pressure is directly proportional to force and inversely proportional to area. Thus, pressure can be increased either by increasing the amount of force or by decreasing the area over which it is applied; pressure can be decreased by decreasing the force or increasing the area.<\/p>\n<p id=\"fs-idm32668544\">Let\u2019s apply this concept to determine which would be more likely to fall through thin ice in <a href=\"#CNX_Chem_09_01_Pressure2\" class=\"autogenerated-content\">Figure 2<\/a>\u2014the elephant or the figure skater? A large African elephant can weigh 7 tons, supported on four feet, each with a diameter of about 1.5 ft (footprint area of 250 in<sup>2<\/sup>), so the pressure exerted by each foot is about 14 lb\/in<sup>2<\/sup>:<\/p>\n<div class=\"equation\" id=\"fs-idm100445488\" style=\"text-align: center\">[latex]\\text{pressure per elephant foot} = 14,000 \\frac{\\text{lb}}{\\text{elephant}} \\times \\frac{1 \\;\\text{elephant}}{4 \\;\\text{feet}} \\times \\frac{1 \\;\\text{foot}}{250 \\;\\text{in}^2} = 14 \\;\\text{lb\/in}^2[\/latex]<\/div>\n<p id=\"fs-idp79686656\">The figure skater weighs about 120 lbs, supported on two skate blades, each with an area of about 2 in<sup>2<\/sup>, so the pressure exerted by each blade is about 30 lb\/in<sup>2<\/sup>:<\/p>\n<div class=\"equation\" id=\"fs-idm181738992\" style=\"text-align: center\">[latex]\\text{pressure per skate blade} = 120 \\frac{\\text{lb}}{\\text{skater}} \\times \\frac{1 \\;\\text{skater}}{2 \\;\\text{blades}} \\times \\frac{1 \\;\\text{blade}}{2 \\;\\text{in}^2} = 30 \\;\\text{lb\/in}^2[\/latex]<\/div>\n<p id=\"fs-idm101012528\">Even though the elephant is more than one hundred-times heavier than the skater, it exerts less than one-half of the pressure and would therefore be less likely to fall though thin ice. On the other hand, if the skater removes her skates and stands with bare feet (or regular footwear) on the ice, the larger area over which her weight is applied greatly reduces the pressure exerted:<\/p>\n<div class=\"equation\" id=\"fs-idp9821216\" style=\"text-align: center\">[latex]\\text{pressure per human foot} = 120 \\frac{\\text{lb}}{\\text{skater}} \\times \\frac{1 \\;\\text{skater}}{2 \\;\\text{feet}} \\times \\frac{1 \\;\\text{foot}}{30 \\;\\text{in}^2} = 2 \\;\\text{lb\/in}^2[\/latex]<\/div>\n<figure id=\"CNX_Chem_09_01_Pressure2\"><figcaption>\n<figure style=\"width: 975px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Pressure2.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Pressure2.jpg\" alt=\"This figure includes two photographs. Figure a is a photo of a large gray elephant on grassy, beige terrain. Figure b is a photo of a figure skater with her right skate on the ice, upper torso lowered, arms extended upward behind her chest, and left leg extended upward behind her.\" width=\"975\" height=\"376\" \/><\/a><figcaption class=\"wp-caption-text\"><strong>Figure 2.<\/strong> Although (a) an elephant\u2019s weight is large, creating a very large force on the ground, (b) the figure skater exerts a much higher pressure on the ice due to the small surface area of her skates. (credit a: modification of work by Guido da Rozze; credit b: modification of work by Ryosuke Yagi)<\/figcaption><\/figure>\n<\/figcaption><\/figure>\n<p>The SI unit of pressure is the <strong>pascal (Pa)<\/strong>, with 1 Pa = 1 N\/m<sup>2<\/sup>, where N is the newton, a unit of force defined as 1 kg m\/s<sup>2<\/sup>. One pascal is a small pressure; in many cases, it is more convenient to use units of kilopascal (1 kPa = 1000 Pa) or <strong>bar<\/strong> (1 bar = 100,000 Pa). In the United States, pressure is often measured in pounds of force on an area of one square inch\u2014<strong>pounds per square inch (psi)<\/strong>\u2014for example, in car tires. Pressure can also be measured using the unit <strong>atmosphere (atm)<\/strong>, which originally represented the average sea level air pressure at the approximate latitude of Paris (45\u00b0). <a href=\"#fs-idp189967312\" class=\"autogenerated-content\">Table 1<\/a> provides some information on these and a few other common units for pressure measurements<\/p>\n<table id=\"fs-idp189967312\" class=\"span-all\" summary=\"This table has two columns and 10 rows. The first row is a header row, and it labels the columns as \u201cUnit Name and Abbreviation\u201d and \u201cDefinition or Relation to Other Unit.\u201d The first unit name and abbreviation is pascal, and it is abbreviated as P a. The definition or relation to other unit is 1 P a equals N over m squared and recommended I U P A C unit. The next unit name is kilopascal, and it is abbreviated as k P a. The definition or relation to other unit is 1 k P a equals 1000 P a. The next unit name is pounds per square inch, and it is abbreviated as p s i. The definition or relation to other unit is air pressure at sea level is approximately 14.7 p s i. The next unit name is atmosphere, and is is abbreviated as a t m. The definition or relation to other unit is 1 a t m equals 101,325 P a and air pressure at sea level is approximately one a t m. The next unit name is bar, and it is abbreviated as bar or b. The definition or relation to other unit is 1 bar equals 100,000 P a exactly and commonly used in meteorology. The next unit name is millibar, and it is abbreviated as m b a r or m b. The definition or relation to other unit is 1000 m b a r equals one bar. The next unit name is inches of mercury, and it is abbreviated as i n period, H g. The definition or relation to other unit is one i n period H g equals 3386 P a and is used by the aviation industry and also some weather reports. The next unit is torr. The definition or relation to other unit is 1 torr equals 1 over 760 a t m and named after Evangelista Torricelli, inventor of the barometer. The last unit name is millimeters of mercury, and it is abbreviated as m m H g. The definition or relation to other unit is 1 m m H g is approximately 1 torr.\">\n<thead>\n<tr valign=\"top\">\n<th>Unit Name and Abbreviation<\/th>\n<th>Definition or Relation to Other Unit<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td>pascal (Pa)<\/td>\n<td>1 Pa = 1 N\/m<sup>2<\/sup><\/p>\n<div><\/div>\n<p>recommended IUPAC unit<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>kilopascal (kPa)<\/td>\n<td>1 kPa = 1000 Pa<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>pounds per square inch (psi)<\/td>\n<td>air pressure at sea level is ~14.7 psi<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>atmosphere (atm)<\/td>\n<td>1 atm = 101,325 Pa<\/p>\n<div><\/div>\n<p>air pressure at sea level is ~1 atm<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>bar (bar, or b)<\/td>\n<td>1 bar = 100,000 Pa (exactly)<\/p>\n<div><\/div>\n<p>commonly used in meteorology<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>millibar (mbar, or mb)<\/td>\n<td>1000 mbar = 1 bar<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>inches of mercury (in. Hg)<\/td>\n<td>1 in. Hg = 3386 Pa<\/p>\n<div><\/div>\n<p>used by aviation industry, also some weather reports<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>torr<\/td>\n<td>[latex]1 \\;\\text{torr} = \\frac{1}{760} \\;\\text{atm}[\/latex]<\/p>\n<div><\/div>\n<p>named after Evangelista Torricelli, inventor of the barometer<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>millimeters of mercury (mm Hg)<\/td>\n<td>1 mm Hg ~1 torr<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td colspan=\"2\"><strong>Table 1.<\/strong>\u00a0Pressure Units<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"textbox shaded\" id=\"fs-idp156787120\">\n<h3>Example 1<\/h3>\n<p id=\"fs-idm55125200\"><strong>Conversion of Pressure Units<\/strong><br \/>\nThe United States National Weather Service reports pressure in both inches of Hg and millibars. Convert a pressure of 29.2 in. Hg into:<\/p>\n<p id=\"fs-idp142663424\">(a) torr<\/p>\n<p id=\"fs-idp6847648\">(b) atm<\/p>\n<p id=\"fs-idm78213376\">(c) kPa<\/p>\n<p id=\"fs-idp62713296\">(d) mbar<\/p>\n<p id=\"fs-idp32588880\"><strong>Solution<\/strong><br \/>\nThis is a unit conversion problem. The relationships between the various pressure units are given in <a href=\"#fs-idp189967312\" class=\"autogenerated-content\">Table 1<\/a>.<\/p>\n<p id=\"fs-idm19510112\">(a) [latex]29.2 \\;\\rule[0.5ex]{2.2em}{0.1ex}\\hspace{-2.2em}\\text{in Hg} \\times \\frac{25.4 \\;\\rule[0.25ex]{1.2em}{0.1ex}\\hspace{-1.2em}\\text{mm}}{1 \\;\\rule[0.25ex]{0.6em}{0.1ex}\\hspace{-0.6em}\\text{in}} \\times \\frac{1 \\;\\text{torr}}{1 \\;\\rule[0.25ex]{2em}{0.1ex}\\hspace{-2em}\\text{mm Hg}} = 742 \\;\\text{torr}[\/latex]<\/p>\n<p id=\"fs-idm103224224\">(b) [latex]742 \\;\\rule[0.5ex]{1.8em}{0.1ex}\\hspace{-1.8em}\\text{torr} \\times \\frac{1 \\;\\text{atm}}{760 \\;\\rule[0.25ex]{1.2em}{0.1ex}\\hspace{-1.2em}\\text{torr}} = 0.976 \\;\\text{atm}[\/latex]<\/p>\n<p id=\"fs-idp28156048\">(c) [latex]742 \\;\\rule[0.5ex]{1.8em}{0.1ex}\\hspace{-1.8em}\\text{torr} \\times \\frac{101.325 \\;\\text{kPa}}{760 \\;\\rule[0.25ex]{1.0em}{0.1ex}\\hspace{-1.0em}\\text{torr}} = 98.9 \\;\\text{kPa}[\/latex]<\/p>\n<p id=\"fs-idm86928016\">(d) [latex]98.9 \\;\\rule[0.5ex]{1.9em}{0.1ex}\\hspace{-1.9em}\\text{kPa} \\times \\frac{1000 \\;\\rule[0.25ex]{0.9em}{0.1ex}\\hspace{-0.9em}\\text{Pa}}{1 \\;\\rule[0.25ex]{1.1em}{0.1ex}\\hspace{-1.1em}\\text{kPa}} \\times \\frac{1 \\;\\rule[0.25ex]{0.9em}{0.1ex}\\hspace{-0.9em}\\text{bar}}{100,000 \\;\\rule[0.25ex]{1.0em}{0.1ex}\\hspace{-1.0em}\\text{Pa}} \\times \\frac{1000 \\;\\text{mbar}}{1 \\;\\rule[0.25ex]{1.0em}{0.1ex}\\hspace{-1.0em}\\text{bar}} = 989 \\;\\text{mbar}[\/latex]<\/p>\n<p id=\"fs-idm28185008\"><strong>Check Your Learning<\/strong><br \/>\nA typical barometric pressure in Kansas City is 740 torr. What is this pressure in atmospheres, in millimeters of mercury, in kilopascals, and in bar?<\/p>\n<div class=\"textbox shaded\" id=\"fs-idm54955856\">\n<h3 class=\"title\">Answer:<\/h3>\n<p id=\"fs-idp131216672\">0.974 atm; 740 mm Hg; 98.7 kPa; 0.987 bar<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idm69336128\">We can measure atmospheric pressure, the force exerted by the atmosphere on the earth\u2019s surface, with a <strong>barometer<\/strong> (<a href=\"#CNX_Chem_09_01_Barometer\" class=\"autogenerated-content\">Figure 3<\/a>). A barometer is a glass tube that is closed at one end, filled with a nonvolatile liquid such as mercury, and then inverted and immersed in a container of that liquid. The atmosphere exerts pressure on the liquid outside the tube, the column of liquid exerts pressure inside the tube, and the pressure at the liquid surface is the same inside and outside the tube. The height of the liquid in the tube is therefore proportional to the pressure exerted by the atmosphere.<\/p>\n<figure id=\"CNX_Chem_09_01_Barometer\">\n<figure style=\"width: 650px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Barometer.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Barometer.jpg\" alt=\"This figure shows two barometers. The barometer to the left contains a shallow reservoir, or open container, of mercury. A narrow tube extends upward from the reservoir above the reservoir. This tube is sealed at the top. To the right, a second similar setup is shown with a reservoir filled with water. Line segments connect the label \u201cvacuum\u201d to the tops of the two narrow tubes. The tube on the left shows the mercury in the reservoir extending in a column upward in the narrow tube. Similarly, the tube on the right shows the water in the reservoir extending upward into the related narrow tube. Double-headed arrows extend from the surface of each liquid in the reservoir to the top of the liquid in each tube. A narrow column or bar extends from the surface of the reservoir to the same height. This bar is labeled \u201catmospheric pressure.\u201d The level of the water in its tube is significantly higher than the level of mercury in its tube.\" width=\"650\" height=\"647\" \/><\/a><figcaption class=\"wp-caption-text\"><strong>Figure 3.<\/strong> In a barometer, the height, <em>h<\/em>, of the column of liquid is used as a measurement of the air pressure. Using very dense liquid mercury (left) permits the construction of reasonably sized barometers, whereas using water (right) would require a barometer more than 30 feet tall.<\/figcaption><\/figure>\n<\/figure>\n<p id=\"fs-idm79676464\">If the liquid is water, normal atmospheric pressure will support a column of water over 10 meters high, which is rather inconvenient for making (and reading) a barometer. Because mercury (Hg) is about 13.6-times denser than water, a mercury barometer only needs to be [latex]\\frac{1}{13.6}[\/latex] as tall as a water barometer\u2014a more suitable size. Standard atmospheric pressure of 1 atm at sea level (101,325 Pa) corresponds to a column of mercury that is about 760 mm (29.92 in.) high. The <strong>torr<\/strong> was originally intended to be a unit equal to one millimeter of mercury, but it no longer corresponds exactly. The pressure exerted by a fluid due to gravity is known as <strong>hydrostatic pressure<\/strong>, <em>p<\/em>:<\/p>\n<div class=\"equation\" id=\"fs-idm35258720\" style=\"text-align: center\">[latex]p = h\\rho g[\/latex]<\/div>\n<p id=\"fs-idm61000288\">where <em>h<\/em> is the height of the fluid, <em>\u03c1<\/em> is the density of the fluid, and <em>g<\/em> is acceleration due to gravity.<\/p>\n<div class=\"textbox shaded\" id=\"fs-idm5509408\">\n<h3>Example 2<\/h3>\n<p id=\"fs-idm124424064\"><strong>Calculation of Barometric Pressure<\/strong><br \/>\nShow the calculation supporting the claim that atmospheric pressure near sea level corresponds to the pressure exerted by a column of mercury that is about 760 mm high. The density of mercury = 13.6 g\/cm<sup>3<\/sup>.<\/p>\n<p id=\"fs-idm64631536\"><strong>Solution<\/strong><br \/>\nThe hydrostatic pressure is given by <em>p<\/em> = <em>h\u03c1g<\/em>, with <em>h<\/em> = 760 mm, <em>\u03c1<\/em> = 13.6 g\/cm<sup>3<\/sup>, and <em>g<\/em> = 9.81 m\/s<sup>2<\/sup>. Plugging these values into the equation and doing the necessary unit conversions will give us the value we seek. (Note: We are expecting to find a pressure of ~101,325 Pa:)<\/p>\n<div class=\"equation\" id=\"fs-idm207611040\" style=\"text-align: center\">[latex]101,325 N\/ \\text{m}^2 = 101,325 \\frac{\\text{kg} \\cdot \\text{m\/s}^2}{\\text{m}^2} = 101,325 \\frac{\\text{kg}}{\\text{m} \\cdot \\text{s}^2}[\/latex]<\/div>\n<div class=\"equation\" id=\"fs-idm149736288\" style=\"text-align: center\">[latex]\\begin{array}{l @{{}={}}l} p & (760 \\;\\text{mm} \\times \\frac{1 \\;\\text{m}}{1000 \\;\\text{mm}}) \\times (\\frac{13.6 \\;\\text{g}}{1 \\;\\text{cm}^3} \\times \\frac{1 \\;\\text{kg}}{1000 \\;\\text{g}} \\times \\frac{(100 \\;\\text{cm})^3}{(1 \\;\\text{m})^3}) \\times (\\frac{9.81 \\;\\text{m}}{1 \\;\\text{s}^2}) \\\\[1em] & (0.760 \\;\\text{m}) (13,600 \\;\\text{kg\/m}^3) (9.81 \\;\\text{m\/s}^2) = 1.01 \\times 10^5 \\;\\text{kg\/ms}^2 = 1.01 \\times 10^5 \\;N\/ \\text{m}^2 \\\\[1em] & 1.01 \\times 10^5 \\;\\text{Pa} \\end{array}[\/latex]<\/div>\n<p id=\"fs-idp70400640\"><strong>Check Your Learning<\/strong><br \/>\nCalculate the height of a column of water at 25 \u00b0C that corresponds to normal atmospheric pressure. The density of water at this temperature is 1.0 g\/cm<sup>3<\/sup>.<\/p>\n<div class=\"textbox shaded\" id=\"fs-idp73341600\">\n<h3 class=\"title\">Answer:<\/h3>\n<p id=\"fs-idp2146864\">10.3 m<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idp189718992\">A <strong>manometer<\/strong> is a device similar to a barometer that can be used to measure the pressure of a gas trapped in a container. A closed-end manometer is a U-shaped tube with one closed arm, one arm that connects to the gas to be measured, and a nonvolatile liquid (usually mercury) in between. As with a barometer, the distance between the liquid levels in the two arms of the tube (<em>h<\/em> in the diagram) is proportional to the pressure of the gas in the container. An open-end manometer (<a href=\"#CNX_Chem_09_01_Manometer\" class=\"autogenerated-content\">Figure 4<\/a>) is the same as a closed-end manometer, but one of its arms is open to the atmosphere. In this case, the distance between the liquid levels corresponds to the difference in pressure between the gas in the container and the atmosphere.<\/p>\n<figure id=\"CNX_Chem_09_01_Manometer\"><figcaption>\n<figure style=\"width: 1300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Manometer.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer.jpg\" alt=\"Three diagrams of manometers are shown. Each manometer consists of a spherical pink container filled with gas on the left that is connected to a U-shaped, sealed tube by a valve on its right. The top of the U-shape aligns with the gas-filled sphere and the U, which extends below, contains mercury. The first manometer has a sealed tube. The sealed end to the upper right in the diagram is labeled \u201cclosed end\u201d and \u201cvacuum.\u201d An arrow points downward in the left side of the U shaped tube to the mercury surface. This arrow is labeled \u201cP subscript gas.\u201d The mercury level is higher in the right side of the tube than in the left. The difference in height is labeled \u201ch.\u201d Beneath this manometer illustration appears the label P subscript gas equal sign h rho g. The second manometer has an open ended tube, which is labeled \u201copen end.\u201d At this opening in the upper right of the diagram is a downward arrow, above which is the label P subscript a t m. An arrow points downward in the left side of the U shaped tube to the mercury surface. This arrow is labeled \u201cP subscript gas.\u201d The mercury level is higher in the left side of the tube than in the right. This difference in height is labeled \u201ch.\u201d Beneath this manometer illustration appears the label P subscript gas equal sign P subscript a t m minus sign h rho g. The third manometer has an open ended tube and is similar to the second manometer except that mercury level is higher in the right side of the tube than in the left. This difference in height is labeled \u201ch.\u201d Beneath this manometer illustration appears the label P subscript gas equal sign P subscript a t m plus h rho g.\" width=\"1300\" height=\"456\" \/><\/a><figcaption class=\"wp-caption-text\"><strong>Figure 4.<\/strong> A manometer can be used to measure the pressure of a gas. The (difference in) height between the liquid levels (<em>h<\/em>) is a measure of the pressure. Mercury is usually used because of its large density.<\/figcaption><\/figure>\n<\/figcaption><\/figure>\n<div class=\"textbox shaded\" id=\"fs-idm31201088\">\n<h3>Example 3<\/h3>\n<p id=\"fs-idp5332928\"><strong>Calculation of Pressure Using a Closed-End Manometer<\/strong><br \/>\nThe pressure of a sample of gas is measured with a closed-end manometer, as shown to the right. The liquid in the manometer is mercury. Determine the pressure of the gas in:<\/p>\n<p id=\"fs-idp161989312\">(a) torr<\/p>\n<p id=\"fs-idp16104736\">(b) Pa<\/p>\n<p id=\"fs-idm85992448\">(c) bar<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer1_img.jpg\" alt=\"A diagram of a closed-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201cclosed end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height between the left side and right side is 26.4 c m which is indicated with horizontal line segments and arrows.\" \/><\/p>\n<p id=\"fs-idm79648128\"><strong>Solution<\/strong><br \/>\nThe pressure of the gas is equal to a column of mercury of height 26.4 cm. (The pressure at the bottom horizontal line is equal on both sides of the tube. The pressure on the left is due to the gas and the pressure on the right is due to 26.4 cm Hg, or mercury.) We could use the equation <em>p<\/em> = <em>h\u03c1g<\/em> as in <a href=\"#fs-idm5509408\" class=\"autogenerated-content\">Example 2<\/a>, but it is simpler to just convert between units using <a href=\"#fs-idp189967312\" class=\"autogenerated-content\">Table 1<\/a>.<\/p>\n<p id=\"fs-idm79108064\">(a) [latex]26.4 \\;\\rule[0.5ex]{2.8em}{0.1ex}\\hspace{-2.8em}\\text{cm Hg} \\times \\frac{10 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}}{1 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}} \\times \\frac{1 \\;\\text{torr}}{1 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}} = 264 \\;\\text{torr}[\/latex]<\/p>\n<p id=\"fs-idp62655904\">(b) [latex]264 \\;\\rule[0.5ex]{1.7em}{0.1ex}\\hspace{-1.7em}\\text{torr} \\times \\frac{1 \\;\\rule[0.25ex]{1.3em}{0.1ex}\\hspace{-1.3em}\\text{atm}}{760 \\;\\rule[0.25ex]{1.3em}{0.1ex}\\hspace{-1.3em}\\text{torr}} \\times \\frac{101,325 \\;\\text{Pa}}{1 \\;\\rule[0.25ex]{1.3em}{0.1ex}\\hspace{-1,3em}\\text{atm}} = 35,200 \\;\\text{Pa}[\/latex]<\/p>\n<p id=\"fs-idp2045200\">(c) [latex]35,200 \\;\\rule[0.5ex]{1.2em}{0.1ex}\\hspace{-1.2em}\\text{Pa} \\times \\frac{1 \\;\\text{bar}}{100,000 \\;\\rule[0.25ex]{1em}{0.1ex}\\hspace{-1em}\\text{Pa}} = 0.352 \\;\\text{bar}[\/latex]<\/p>\n<p id=\"fs-idp37894320\"><strong>Check Your Learning<\/strong><br \/>\nThe pressure of a sample of gas is measured with a closed-end manometer. The liquid in the manometer is mercury. Determine the pressure of the gas in:<\/p>\n<p id=\"fs-idp38024128\">(a) torr<\/p>\n<p id=\"fs-idp16117232\">(b) Pa<\/p>\n<p id=\"fs-idp127919232\">(c) bar<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer2_img.jpg\" alt=\"A diagram of a closed-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201cclosed end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 6.0 i n is indicated with horizontal line segments and arrows.\" \/><\/p>\n<div class=\"textbox shaded\" id=\"fs-idm70430576\">\n<h3 class=\"title\">Answer:<\/h3>\n<p id=\"fs-idm8669760\">(a) ~150 torr; (b) ~20,000 Pa; (c) ~0.20 bar<\/p>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\" id=\"fs-idm76587328\">\n<h3>Example\u00a04<\/h3>\n<p id=\"fs-idm12992864\"><strong>Calculation of Pressure Using an Open-End Manometer<\/strong><br \/>\nThe pressure of a sample of gas is measured at sea level with an open-end Hg (mercury) manometer, as shown to the right. Determine the pressure of the gas in:<\/p>\n<p id=\"fs-idp141807120\">(a) mm Hg<\/p>\n<p id=\"fs-idm91216192\">(b) atm<\/p>\n<p id=\"fs-idm29337808\">(c) kPa<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer3_img.jpg\" alt=\"A diagram of an opne-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 13.7 c m is indicated with horizontal line segments and arrows.\" \/><\/p>\n<p id=\"fs-idp6251232\"><strong>Solution<\/strong><br \/>\nThe pressure of the gas equals the hydrostatic pressure due to a column of mercury of height 13.7 cm plus the pressure of the atmosphere at sea level. (The pressure at the bottom horizontal line is equal on both sides of the tube. The pressure on the left is due to the gas and the pressure on the right is due to 13.7 cm of Hg plus atmospheric pressure.)<\/p>\n<p id=\"fs-idp139076928\">(a) In mm Hg, this is: 137 mm Hg + 760 mm Hg = 897 mm Hg<\/p>\n<p id=\"fs-idm20839232\">(b) [latex]897 \\;\\rule[0.5ex]{3em}{0.1ex}\\hspace{-3em}\\text{mm Hg} \\times \\frac{1 \\;\\text{atm}}{760 \\;\\rule[0.25ex]{2.5em}{0.1ex}\\hspace{-2.5em}\\text{mm Hg}} = 1.18 \\;\\text{atm}[\/latex]<\/p>\n<p id=\"fs-idp8049056\">(c) [latex]1.18 \\;\\rule[0.5ex]{1.8em}{0.1ex}\\hspace{-1.8em}\\text{atm} \\times \\frac{101.325 \\;\\text{kPa}}{1 \\;\\rule[0.25ex]{1.5em}{0.1ex}\\hspace{-1.5em}\\text{atm}} = 1.20 \\times 10^2 \\;\\text{kPa}[\/latex]<\/p>\n<p id=\"fs-idm24876576\"><strong>Check Your Learning<\/strong><br \/>\nThe pressure of a sample of gas is measured at sea level with an open-end Hg manometer, as shown to the right. Determine the pressure of the gas in:<\/p>\n<p id=\"fs-idp30718048\">(a) mm Hg<\/p>\n<p id=\"fs-idm5192960\">(b) atm<\/p>\n<p id=\"fs-idp18503824\">(c) kPa<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_manometer4_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the left side than on the right. The difference in height of 4.63 i n is indicated with horizontal line segments and arrows.\" \/><\/p>\n<div class=\"textbox shaded\" id=\"fs-idp173017200\">\n<h3 class=\"title\">Answer:<\/h3>\n<p id=\"fs-idp154771664\">(a) 642 mm Hg; (b) 0.845 atm; (c) 85.6 kPa<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idp183412160\" class=\"textbox shaded\">\n<h3 class=\"title\">Measuring Blood Pressure<\/h3>\n<p id=\"fs-idm61054480\">Blood pressure is measured using a device called a sphygmomanometer (Greek <em>sphygmos<\/em> = \u201cpulse\u201d). It consists of an inflatable cuff to restrict blood flow, a manometer to measure the pressure, and a method of determining when blood flow begins and when it becomes impeded (<a href=\"#CNX_Chem_09_01_Spygmo\" class=\"autogenerated-content\">Figure 5<\/a>). Since its invention in 1881, it has been an essential medical device. There are many types of sphygmomanometers: manual ones that require a stethoscope and are used by medical professionals; mercury ones, used when the most accuracy is required; less accurate mechanical ones; and digital ones that can be used with little training but that have limitations. When using a sphygmomanometer, the cuff is placed around the upper arm and inflated until blood flow is completely blocked, then slowly released. As the heart beats, blood forced through the arteries causes a rise in pressure. This rise in pressure at which blood flow begins is the <em>systolic pressure\u2014<\/em>the peak pressure in the cardiac cycle. When the cuff\u2019s pressure equals the arterial systolic pressure, blood flows past the cuff, creating audible sounds that can be heard using a stethoscope. This is followed by a decrease in pressure as the heart\u2019s ventricles prepare for another beat. As cuff pressure continues to decrease, eventually sound is no longer heard; this is the <em>diastolic pressure\u2014<\/em>the lowest pressure (resting phase) in the cardiac cycle. Blood pressure units from a sphygmomanometer are in terms of millimeters of mercury (mm Hg).<\/p>\n<figure id=\"CNX_Chem_09_01_Spygmo\"><figcaption>\n<figure style=\"width: 975px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Spygmo.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Spygmo.jpg\" alt=\"This figure includes two photographs. The first photo shows a young adult male placing a blood pressure cuff on the upper arm of a young adult female. The second image shows a typical sphygmomanometer, which includes a black blood pressure cuff, tubing, pump, and pressure gauge.\" width=\"975\" height=\"313\" \/><\/a><figcaption class=\"wp-caption-text\"><strong>Figure 5.<\/strong> (a) A medical technician prepares to measure a patient\u2019s blood pressure with a sphygmomanometer. (b) A typical sphygmomanometer uses a valved rubber bulb to inflate the cuff and a diaphragm gauge to measure pressure. (credit a: modification of work by Master Sgt. Jeffrey Allen)<\/figcaption><\/figure>\n<\/figcaption><\/figure>\n<\/div>\n<div id=\"fs-idm96003696\" class=\"textbox shaded\">\n<h3 class=\"title\">Meteorology, Climatology, and Atmospheric Science<\/h3>\n<p id=\"fs-idm77491200\">Throughout the ages, people have observed clouds, winds, and precipitation, trying to discern patterns and make predictions: when it is best to plant and harvest; whether it is safe to set out on a sea voyage; and much more. We now face complex weather and atmosphere-related challenges that will have a major impact on our civilization and the ecosystem. Several different scientific disciplines use chemical principles to help us better understand weather, the atmosphere, and climate. These are meteorology, climatology, and atmospheric science. Meteorology is the study of the atmosphere, atmospheric phenomena, and atmospheric effects on earth\u2019s weather. Meteorologists seek to understand and predict the weather in the short term, which can save lives and benefit the economy. Weather forecasts (<a href=\"#CNX_Chem_09_01_WeatherMap\" class=\"autogenerated-content\">Figure 6<\/a>) are the result of thousands of measurements of air pressure, temperature, and the like, which are compiled, modeled, and analyzed in weather centers worldwide.<\/p>\n<figure id=\"CNX_Chem_09_01_WeatherMap\">\n<figure style=\"width: 650px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_WeatherMap.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_WeatherMap.jpg\" alt=\"A weather map of the United States is shown which points out areas of high and low pressure with the letters H in blue and L in red. Curved lines in grey, orange, blue, and red are shown. The orange lines are segmented. The red and blue lines have small red or blue semi-circles and triangles attached along their lengths. In dashed white lines, latitude and longitude are indicated. Underlined three and four digit numbers also appear across the map.\" width=\"650\" height=\"402\" \/><\/a><figcaption class=\"wp-caption-text\"><strong>Figure 6.<\/strong> Meteorologists use weather maps to describe and predict weather. Regions of high (H) and low (L) pressure have large effects on weather conditions. The gray lines represent locations of constant pressure known as isobars. (credit: modification of work by National Oceanic and Atmospheric Administration)<\/figcaption><\/figure>\n<\/figure>\n<p id=\"fs-idm8048304\">In terms of weather, low-pressure systems occur when the earth\u2019s surface atmospheric pressure is lower than the surrounding environment: Moist air rises and condenses, producing clouds. Movement of moisture and air within various weather fronts instigates most weather events.<\/p>\n<p id=\"fs-idm49021728\">The atmosphere is the gaseous layer that surrounds a planet. Earth\u2019s atmosphere, which is roughly 100\u2013125 km thick, consists of roughly 78.1% nitrogen and 21.0% oxygen, and can be subdivided further into the regions shown in <a href=\"#CNX_Chem_09_01_Atmosphere\" class=\"autogenerated-content\">Figure 7<\/a>: the exosphere (furthest from earth, &gt; 700 km above sea level), the thermosphere (80\u2013700 km), the mesosphere (50\u201380 km), the stratosphere (second lowest level of our atmosphere, 12\u201350 km above sea level), and the troposphere (up to 12 km above sea level, roughly 80% of the earth\u2019s atmosphere by mass and the layer where most weather events originate). As you go higher in the troposphere, air density and temperature both decrease.<\/p>\n<figure id=\"CNX_Chem_09_01_Atmosphere\"><figcaption>\n<figure style=\"width: 1200px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/chemistry\/wp-content\/uploads\/sites\/150\/2016\/05\/CNX_Chem_09_01_Atmosphere.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Atmosphere.jpg\" alt=\"This diagram shows half of a two dimensional view of the earth in blue and green. A narrow white layer, labeled \u201ctroposphere 0 dash 12 k m\u201d covers this hemisphere. This layer is also labeled \u201clayer where most weather events originate.\u201d Next, a thicker light blue layer labeled \u201cStratosphere 12 dash 50 k m\u201d is shown. This is followed by a slightly thinner layer also in light blue labeled \u201cMesosphere 50 dash 80 k m.\u201d Following this layer is a relatively thick light blue layer labeled \u201cThermosphere 80 dash 700 k m.\u201d A blue layer appears that covers the rightmost two thirds of the diagram. This region gradually darkens from a lighter blue at the left to a dark blue at the right. This region of the diagram is labeled \u201cexosphere greater than 700 k m.\u201d\" width=\"1200\" height=\"547\" \/><\/a><figcaption class=\"wp-caption-text\"><strong> Figure 7.<\/strong> Earth\u2019s atmosphere has five layers: the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.<\/figcaption><\/figure>\n<\/figcaption><\/figure>\n<p id=\"fs-idm30549520\">Climatology is the study of the climate, averaged weather conditions over long time periods, using atmospheric data. However, climatologists study patterns and effects that occur over decades, centuries, and millennia, rather than shorter time frames of hours, days, and weeks like meteorologists. Atmospheric science is an even broader field, combining meteorology, climatology, and other scientific disciplines that study the atmosphere.<\/p>\n<\/div>\n<section id=\"fs-idm62097440\" class=\"summary\">\n<h1>Key Concepts and Summary<\/h1>\n<p id=\"fs-idm102779232\">Gases exert pressure, which is force per unit area. The pressure of a gas may be expressed in the SI unit of pascal or kilopascal, as well as in many other units including torr, atmosphere, and bar. Atmospheric pressure is measured using a barometer; other gas pressures can be measured using one of several types of manometers.<\/p>\n<\/section>\n<section id=\"fs-idp68662112\" class=\"key-equations\">\n<h1>Key Equations<\/h1>\n<ul id=\"fs-idm103206560\">\n<li>[latex]P = \\frac{F}{A}[\/latex]<\/li>\n<li>[latex]p = h \\rho g[\/latex]<\/li>\n<\/ul>\n<\/section>\n<section id=\"fs-idm20163680\" class=\"exercises\">\n<div class=\"bcc-box bcc-info\">\n<h3 itemprop=\"educationalUse\">Chemistry End of Chapter Exercises<\/h3>\n<ol>\n<li id=\"fs-idm19553744\">Why are sharp knives more effective than dull knives (Hint: think about the definition of pressure)?<\/li>\n<li id=\"fs-idp62697024\">Why do some small bridges have weight limits that depend on how many wheels or axles the crossing vehicle has?<\/li>\n<li id=\"fs-idm50132240\">Why should you roll or belly-crawl rather than walk across a thinly-frozen pond?<\/li>\n<li id=\"fs-idm137597392\">A typical barometric pressure in Redding, California, is about 750 mm Hg. Calculate this pressure in atm and kPa.<\/li>\n<li id=\"fs-idp3670784\">A typical barometric pressure in Denver, Colorado, is 615 mm Hg. What is this pressure in atmospheres and kilopascals?<\/li>\n<li id=\"fs-idp135739664\">A typical barometric pressure in Kansas City is 740 torr. What is this pressure in atmospheres, in millimeters of mercury, and in kilopascals?<\/li>\n<li id=\"fs-idp38342496\">Canadian tire pressure gauges are marked in units of kilopascals. What reading on such a gauge corresponds to 32 psi?<\/li>\n<li id=\"fs-idm38508352\">During the Viking landings on Mars, the atmospheric pressure was determined to be on the average about 6.50 millibars (1 bar = 0.987 atm). What is that pressure in torr and kPa?<\/li>\n<li id=\"fs-idm88643488\">The pressure of the atmosphere on the surface of the planet Venus is about 88.8 atm. Compare that pressure in psi to the normal pressure on earth at sea level in psi.<\/li>\n<li id=\"fs-idm38299280\">A medical laboratory catalog describes the pressure in a cylinder of a gas as 14.82 MPa. What is the pressure of this gas in atmospheres and torr?<\/li>\n<li id=\"fs-idp39879760\">Consider this scenario and answer the following questions: On a mid-August day in the northeastern United States, the following information appeared in the local newspaper: atmospheric pressure at sea level 29.97 in., 1013.9 mbar.\n<p id=\"fs-idm50271520\">(a) What was the pressure in kPa?<\/p>\n<p id=\"fs-idp189723312\">(b) The pressure near the seacoast in the northeastern United States is usually reported near 30.0 in. Hg. During a hurricane, the pressure may fall to near 28.0 in. Hg. Calculate the drop in pressure in torr.<\/p>\n<\/li>\n<li id=\"fs-idp26220160\">Why is it necessary to use a nonvolatile liquid in a barometer or manometer?<\/li>\n<li id=\"fs-idm29763808\">The pressure of a sample of gas is measured at sea level with a closed-end manometer. The liquid in the manometer is mercury. Determine the pressure of the gas in:\n<p id=\"fs-idp89607040\">(a) torr<\/p>\n<p id=\"fs-idm95742832\">(b) Pa<\/p>\n<p id=\"fs-idm80328752\">(c) bar<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer5_img.jpg\" alt=\"A diagram of a closed-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201cclosed end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 26.4 c m is indicated with horizontal line segments and arrows.\" \/><\/li>\n<li id=\"fs-idp185367488\">The pressure of a sample of gas is measured with an open-end manometer, partially shown to the right. The liquid in the manometer is mercury. Assuming atmospheric pressure is 29.92 in. Hg, determine the pressure of the gas in:\n<p id=\"fs-idm39627648\">(a) torr<\/p>\n<p id=\"fs-idp27090112\">(b) Pa<\/p>\n<p id=\"fs-idm69293536\">(c) bar<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer6_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the left side than on the right. The difference in height of 6.00 i n is indicated with horizontal line segments and arrows.\" \/><\/li>\n<li id=\"fs-idm86041584\">The pressure of a sample of gas is measured at sea level with an open-end mercury manometer. Assuming atmospheric pressure is 760.0 mm Hg, determine the pressure of the gas in:\n<p id=\"fs-idp164256000\">(a) mm Hg<\/p>\n<p id=\"fs-idp142813824\">(b) atm<\/p>\n<p id=\"fs-idp30379328\">(c) kPa<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer7_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the left side than on the right. The difference in height of 13.7 c m is indicated with horizontal line segments and arrows.\" \/><\/li>\n<li>The pressure of a sample of gas is measured at sea level with an open-end mercury manometer. Assuming atmospheric pressure is 760 mm Hg, determine the pressure of the gas in:\n<p id=\"fs-idm77467552\">(a) mm Hg<\/p>\n<p id=\"fs-idm90142112\">(b) atm<\/p>\n<p id=\"fs-idp189802448\">(c) kPa<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-content\/uploads\/sites\/309\/2018\/01\/CNX_Chem_09_01_Manometer8_img.jpg\" alt=\"A diagram of an open-end manometer is shown. To the upper left is a spherical container labeled, \u201cgas.\u201d This container is connected by a valve to a U-shaped tube which is labeled \u201copen end\u201d at the upper right end. The container and a portion of tube that follows are shaded pink. The lower portion of the U-shaped tube is shaded grey with the height of the gray region being greater on the right side than on the left. The difference in height of 26.4 c m is indicated with horizontal line segments and arrows.\" \/><\/li>\n<li id=\"fs-idm79130144\">How would the use of a volatile liquid affect the measurement of a gas using open-ended manometers vs. closed-end manometers?<\/li>\n<\/ol>\n<\/div>\n<\/section>\n<div>\n<h2>Glossary<\/h2>\n<dl id=\"fs-idm92046304\" class=\"definition\">\n<dt>atmosphere (atm)<\/dt>\n<dd id=\"fs-idm48979616\">unit of pressure; 1 atm = 101,325 Pa<\/dd>\n<\/dl>\n<dl id=\"fs-idm49164816\" class=\"definition\">\n<dt>bar<\/dt>\n<dd id=\"fs-idm19523424\">(bar or b) unit of pressure; 1 bar = 100,000 Pa<\/dd>\n<\/dl>\n<dl id=\"fs-idp128557152\" class=\"definition\">\n<dt>barometer<\/dt>\n<dd id=\"fs-idp44432976\">device used to measure atmospheric pressure<\/dd>\n<\/dl>\n<dl id=\"fs-idp1898224\" class=\"definition\">\n<dt>hydrostatic pressure<\/dt>\n<dd id=\"fs-idm78041232\">pressure exerted by a fluid due to gravity<\/dd>\n<\/dl>\n<dl id=\"fs-idm30126128\" class=\"definition\">\n<dt>manometer<\/dt>\n<dd id=\"fs-idm91258448\">device used to measure the pressure of a gas trapped in a container<\/dd>\n<\/dl>\n<dl id=\"fs-idm69533872\" class=\"definition\">\n<dt>pascal (Pa)<\/dt>\n<dd id=\"fs-idm53495904\">SI unit of pressure; 1 Pa = 1 N\/m<sup>2<\/sup><\/dd>\n<\/dl>\n<dl id=\"fs-idm87137504\" class=\"definition\">\n<dt>pounds per square inch (psi)<\/dt>\n<dd id=\"fs-idm52430016\">unit of pressure common in the US<\/dd>\n<\/dl>\n<dl id=\"fs-idm61385376\" class=\"definition\">\n<dt>pressure<\/dt>\n<dd id=\"fs-idm64654544\">force exerted per unit area<\/dd>\n<\/dl>\n<dl id=\"fs-idm23965520\" class=\"definition\">\n<dt>torr<\/dt>\n<dd id=\"fs-idm55637456\">unit of pressure; [latex]1 \\;\\text{torr} = \\frac{1}{760} \\;\\text{atm}[\/latex]<\/dd>\n<\/dl>\n<\/div>\n<div class=\"bcc-box bcc-info\">\n<h3 itemprop=\"educationalUse\">Solutions<\/h3>\n<p><strong>Answers to Chemistry End of Chapter Exercises<\/strong><\/p>\n<p id=\"fs-idm33698016\">1. The cutting edge of a knife that has been sharpened has a smaller surface area than a dull knife. Since pressure is force per unit area, a sharp knife will exert a higher pressure with the same amount of force and cut through material more effectively.<\/p>\n<p id=\"fs-idp69163280\">3. Lying down distributes your weight over a larger surface area, exerting less pressure on the ice compared to standing up. If you exert less pressure, you are less likely to break through thin ice.<\/p>\n<p id=\"fs-idm25200320\">5. 0.809 atm; 82.0 kPa<\/p>\n<p id=\"fs-idm5145968\">7. 2.2 \u00d7 10<sup>2<\/sup> kPa<\/p>\n<p id=\"fs-idp86259712\">9. Earth: 14.7 lb in<sup>\u20132<\/sup>; Venus: 13.1 \u00d7 10<sup>3<\/sup> lb in<sup>\u22122<\/sup><\/p>\n<p id=\"fs-idm21108080\">11. (a) 101.5 kPa; (b) 51 torr drop<\/p>\n<p id=\"fs-idm83006352\">13. (a) 264 torr; (b) 35,200 Pa; (c) 0.352 bar<\/p>\n<p id=\"fs-idm33920592\">15. (a) 623 mm Hg; (b) 0.820 atm; (c) 83.1 kPa<\/p>\n<p id=\"fs-idm51906080\">17. With a closed-end manometer, no change would be observed, since the vaporized liquid would contribute equal, opposing pressures in both arms of the manometer tube. However, with an open-ended manometer, a higher pressure reading of the gas would be obtained than expected, since <em>P<\/em><sub>gas<\/sub> = <em>P<\/em><sub>atm<\/sub> + <em>P<\/em><sub>vol liquid<\/sub>.<\/p>\n<\/div>\n","protected":false},"author":103,"menu_order":2,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-590","chapter","type-chapter","status-publish","hentry"],"part":571,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/pressbooks\/v2\/chapters\/590","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/wp\/v2\/users\/103"}],"version-history":[{"count":2,"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/pressbooks\/v2\/chapters\/590\/revisions"}],"predecessor-version":[{"id":1481,"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/pressbooks\/v2\/chapters\/590\/revisions\/1481"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/pressbooks\/v2\/parts\/571"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/pressbooks\/v2\/chapters\/590\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/wp\/v2\/media?parent=590"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/pressbooks\/v2\/chapter-type?post=590"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/wp\/v2\/contributor?post=590"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/chemistryrichardson\/wp-json\/wp\/v2\/license?post=590"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}