6.5 End of Chapter Problems

1. Chemical equations can also be used to represent physical processes. Write a chemical equation for the boiling of water, including the proper phase labels.

2. Chemical equations can also be used to represent physical processes. Write a chemical equation for the freezing of water, including the proper phase labels.

3. Explain why the following chemical equation should not be considered a proper chemical equation:

a)  N₂      b)  NH₃      c)  NO      d)  N₂O

e)  NO₂      f)  N₂O₄      g)  N₂O₅      h)  NaNO₃

15. Write the unbalanced chemical equation for each of the following reactions.

a) solid mercury(II) oxide decomposes to produce liquid mercury metal and gaseous oxygen.

b) Solid zinc metal reacts with hydrochloric acid to produce zinc chloride dissolved in water and hydrogen gas.

c) Propane (C₃H₈) gas reacts with oxygen in air to produce gaseous carbon dioxide and water vapor.

d) Solid ammonium nitrate can be produced by bubbling ammonia gas through nitric acid solution.

e) Elemental boron can be produced by heating solid diboron trioxide with magnesium metal, also producing solid magnesium oxide as a by-product.

16. Beneath each word equation, write the formula equation and balance it:

a) zinc + sulfuric acid  $\longrightarrow$  zinc sulfate + hydrogen

b) carbon + oxygen  $\longrightarrow$  carbon dioxide

c) hydrogen + oxygen  $\longrightarrow$  water

d)  aluminum + hydrochloric acid  $\longrightarrow$ aluminum chloride + hydrogen

e) chromium + oxygen  $\longrightarrow$ chromium(III) oxide

f) potassium + water  $\longrightarrow$  potassium hydroxide + hydrogen

g) copper(II) oxide + hydrochloric acid $\longrightarrow$  copper(II) chloride + water 

h) sodium hydrogen carbonate + nitric acid $\longrightarrow$  sodium nitrate + water + carbon dioxide

17. Balance the following equations:

a) H₃PO₄  +  CaO $\longrightarrow$ Ca₃(PO₄)₂  +  H₂O                    

b) NH₃  +  O₂ $\longrightarrow$ NO₂  +  H₂O

c) Cl₂O₇  +  H₂O $\longrightarrow$ HClO₄                                       

d) Mg₃N₂  +  H₂O $\longrightarrow$ Mg(OH)₂  +  NH₃

e) FeSO₄ $\longrightarrow$ Fe₂O₃  +  SO₂  +  O₂                             

f)P₄  +  Cl₂ $\longrightarrow$ PCl₃

g) MnO₂  +  C $\longrightarrow$ Mn  +  CO₂                                     

h) Na₂O₂  +  H₂O $\longrightarrow$ NaOH   +  O₂

i) CaH₂  +  H₂O $\longrightarrow$ Ca(OH)₂  +  H₂                             

j)NaHCO₃ $\longrightarrow$ Na₂CO₃  +  CO₂  +  H₂O

18. Balance the following equations:

a)  Mg  +  O₂  $\longrightarrow$ MgO                                          

b)  KClO₃  $\longrightarrow$ KCl  +  O₂

c)  Fe  +  O₂  $\longrightarrow$ Fe₃O₄                                         

d)  Mg +  HCl  $\longrightarrow$ MgCl₂  +  H₂

e)  Na  +  H₂O  $\longrightarrow$ NaOH  +  H₂                            

f)  N₂+  H₂ $\longrightarrow$ NH₃

g)  Na₂CO₃•10H₂O   $\longrightarrow$  Na₂CO₃+  H₂O               

h)  Fe +  H₂O  $\longrightarrow$ Fe₃O₄+  H₂

i)  F₂  +  H₂O  $\longrightarrow$ HF +  O₂

19. Balance the following chemical equations.

a)   Ca₃(PO₄)₂   +   SiO₂   +   C   $\longrightarrow$    P₄  +    CaSiO₃    +   CO₂

b)   C₂H₆O₂   +   O₃  $\longrightarrow$    CO₂   +   H₂O

c)   Fe₃O₄    +    S₈   $\longrightarrow$  Fe₂S₃   +    SO₃

d)   P₂S₅   +    O₂   $\longrightarrow$ S₈   +    P₃O₈

e)   C₃H₈   +    SO₂ $\longrightarrow$ C₂H₄O₄   +   H₂O   +   S₈

20. Predict whether or not a reaction will occur when each of the following pairs of solutions are mixed. If no reaction occurs, write NR on the right hand side of the equation. If a reaction does occur, complete and balance the equations as molecular equations, and give the balanced complete ionic and net ionic equations as well. Be sure to indicate the states of all reagents.

a)  NaCl(aq)  +  AgNO₃(aq) $\longrightarrow$                        

b)  BaCl₂(aq)  +  H₂SO₄(aq) $\longrightarrow$

c)  FeCl₃(aq)  +  NH₄OH(aq) $\longrightarrow$                       

d)  K₂CrO₄(aq)  + Pb(NO₃)₂(aq) $\longrightarrow$

e)  KClO₃(aq)  +  MgCl₂(aq) $\longrightarrow$                        

f)  (NH₄)₂CO₃(aq)  +  CaCl₂(aq) $\longrightarrow$

g)  NaC₂H₃O₂(aq)  +  BaCl₂(aq) $\longrightarrow$

21. Identify each of the following unbalanced reaction equations as belonging to one or more of the following categories: precipitation, acid-base, or redox.

a)  Fe_(s)+ H₂SO_4(aq) $\longrightarrow$ Fe₃(SO₄)_2(aq)+ H_2(g)

b)  HClO_4(aq)+ RbOH_(aq) $\longrightarrow$ RbClO_4(aq)+ H₂O_(l)

c)  Ca_(s)+ O_2(g) $\longrightarrow$ CaO_(s)

d)  H₂SO_4(aq)+ NaOH_(aq) $\longrightarrow$ Na₂SO_4(aq)+ H₂O_(l)

e)  Pb(NO₃)_2(aq)+ Na₂CO_3(aq) $\longrightarrow$ PbCO_3(s)+ NaNO_3(aq)

f)  K₂SO_4(aq)+ CaCl_2(aq) $\longrightarrow$ KCl_(aq)+ CaSO_4(s)

22. Classify the following unbalanced chemical reactions by as many methods as possible.

a)  I₄O_9(s) $\longrightarrow$ I₂O_6(s)+ I_2(s)+ O_2(g)

b)  Mg_(s)+ AgNO_3(aq) $\longrightarrow$ Mg(NO₃)_2(aq)+ Ag_(s)

c)  SiCl_4(l)+ Mg_(s) $\longrightarrow$ MgCl_2(aq)+ Si_(s)

d)  CuCl_2(aq)+ AgNO_3(aq) $\longrightarrow$ Cu(NO₃)_2(aq)+ AgCl_(s)

e)  Al_(s)+ Br_2(l) $\longrightarrow$ AlBr_3(s)

f)  HBr_(aq)+ NaOH_(aq) $\longrightarrow$ NaBr_(aq)+ H₂O_(l)

Answers

1. H₂O(ℓ) $\longrightarrow$ H₂O(g)

2. H₂O(ℓ) $\longrightarrow$ H₂O(s)

3. The coefficients are not in their lowest whole-number ratio.

4. No; zinc is lower in the activity series than aluminum.

5. In the products, the cation is pairing with the cation, and the anion is pairing with the anion.

6. Ag₂SO₄(aq) + SrCl₂(aq) $\longrightarrow$ SrSO₄(s) + 2 AgCl(s) 

7. Complete ionic equation: Ba²⁺(aq) + 2 Cl⁻(aq) + 2 Ag⁺(aq) + SO₄²⁻(aq) $\longrightarrow$ BaSO₄(s) + 2 AgCl(s)

Net ionic equation: The net ionic equation is the same as the complete ionic equation.

8. Complete ionic equation: Sr²⁺(aq) + 2 Cl⁻(aq) + 2 Ag⁺(aq) + SO₄²⁻(aq) $\longrightarrow$ SrSO₄(s) + 2 AgCl(s)

Net ionic equation: The net ionic equation is the same as the complete ionic equation.

9. Each ion is a spectator ion; there is no overall net ionic equation.

10. Yes; H₂ + Cl₂ $\longrightarrow$ 2 HCl (answers will vary)

11. Yes; 2 HCl $\longrightarrow$ H₂ + Cl₂ (answers will vary)

12. It does not increase the H⁺ ion concentration; it is not a compound of H⁺.

13. a)  0      b)  −3      c)  +2      d)  +1

e)  +4          f) +4        g)  +5      h)  +5

14. Copper is disproportionating. Initially, its oxidation number is +1; in the products, its oxidation numbers are +2 and 0, respectively.

15.   a) HgO(s) $\longrightarrow$ Hg(l) + O₂(g)
b)  Zn(s) + HCl(aq) $\longrightarrow$ ZnCl₂(aq) + H₂(g)
c)  C₃H₈(g) + O₂(g) $\longrightarrow$ CO₂(g) + H₂O(g)
d)  NH₃(g) + HNO₃(aq) $\longrightarrow$ NH₄NO₃(s)
e)  B₂O₃(s) + Mg(s) $\longrightarrow$ B(s) + MgO(s)

16.   a) Zn(s) + H₂SO₄(aq) $\longrightarrow$  ZnSO₄(aq)  +  H₂(g)
b)  C(s) + O₂(g) $\longrightarrow$ CO₂(g)
c)  2H₂(g) + O₂(g)  $\longrightarrow$  2H₂O(l)
d)  2Al(s) + 6HCl(aq)  $\longrightarrow$  2AlCl₃(aq)  +  3H₂(g)
e)  4Cr(s) + 3O₂(g)  $\longrightarrow$  2Cr₂O₃(s)
f)  2K(s) + 2H₂O(aq)  $\longrightarrow$ 2KOH(aq)  +  H₂(g)
g)  CuO(s) + 2HCl(aq)  $\longrightarrow$  CuCl₂(aq) + H₂O(l)
h)  NaHCO₃(aq) + HNO₃(aq)  $\longrightarrow$  NaNO₃(aq)  +  H₂O(l) + CO₂(g)

17.   a)  2H₃PO₄  +  3CaO $\longrightarrow$ Ca₃(PO₄)₂  +  3H₂O
b)  4NH₃  +  7O₂ $\longrightarrow$ 4NO₂  +  6H₂O
c)  Cl₂O₇  +  H₂O $\longrightarrow$ 2HClO₄
d)  Mg₃N₂  +  6H₂O $\longrightarrow$ 3Mg(OH)₂  +  2NH₃
e)  4FeSO₄ $\longrightarrow$ 2Fe₂O₃  +  4SO₂  +  O₂
f)  P₄+ 6Cl₂ $\longrightarrow$ 4PCl₃
g)  MnO₂  +  C $\longrightarrow$ Mn  +  CO₂
h)  2Na₂O₂  +  2H₂O $\longrightarrow$ 4NaOH  +  O₂
i)  CaH₂  +  2H₂O $\longrightarrow$ Ca(OH)₂  +  2H₂
j)  2NaHCO₃ $\longrightarrow$ Na₂CO₃  +  CO₂  +  H₂O

18.   a) 2Mg  +  O₂ $\longrightarrow$ 2MgO
b)  2KClO₃  $\longrightarrow$ 2KCl  +  3O₂
c)  3Fe +  2O₂  $\longrightarrow$ Fe₃O₄
d)  Mg +  2HCl  $\longrightarrow$ MgCl₂  +  H₂
e)  2Na +  2H₂O  $\longrightarrow$ 2NaOH  +  H₂
f)  N₂+  3H₂  $\longrightarrow$ 2NH₃
g)  Na₂CO₃• 10H₂O  $\longrightarrow$ Na₂CO₃+ 10H₂O
h)  3Fe  +  4H₂O  $\longrightarrow$ Fe₃O₄+  4H₂
i)  2F₂  +  2H₂O  $\longrightarrow$ 4HF +  O₂

19. Balance the following chemical equations.

a)  2 Ca₃(PO₄)₂+  6 SiO₂+  5 C  $\longrightarrow$ P₄+ 6 CaSiO₃+ 5 CO₂

b)  3 C₂H₆O₂   +   5 O₃   $\longrightarrow$   6 CO₂   +   9 H₂O

c)  48 Fe₃O₄   +   35 S₈  $\longrightarrow$   72 Fe₂S₃   +   64 SO₃

d)  24 P₂S₅   +  64O₂ $\longrightarrow$ 15 S₈   +   16 P₃O₈

e)  16 C₃H₈  +   56 SO₂ $\longrightarrow$  24 C₂H₄O₄  +  16 H₂O  +  7 S₈

20.  a) NaCl_(aq)+ AgNO_3(aq) $\longrightarrow$ AgCl_(s)+ NaNO_3(aq)
Na⁺_(aq)+ Cl^–_(aq)+ Ag⁺_(aq)+ NO₃^–_(aq)
                           $\longrightarrow$ AgCl_(s)+ Na⁺_(aq)+ NO₃^–_(aq)
Cl^–_(aq)+ Ag⁺_(aq) $\longrightarrow$ AgCl_(s)

b) BaCl_2(aq)+ H₂SO_4(aq) $\longrightarrow$ BaSO_4(s)+ 2HCl_(aq)
Ba²⁺_(aq)+ 2Cl^–_(aq)+ 2H⁺_(aq)+ SO₄^2-_(aq)
                           $\longrightarrow$ BaSO_4(s)+ 2H⁺_(aq)+ 2Cl^–_(aq)
Ba²⁺_(aq)+ SO₄^2-_(aq) $\longrightarrow$ BaSO_4(s)

c) FeCl_3(aq)+ 3NH₄OH_(aq) $\longrightarrow$ Fe(OH)_3(s)+ 3NH₄Cl_(aq)
Fe³⁺_(aq)+ 3Cl^–_(aq)+ 3 NH₄⁺_(aq)+ 3OH^–_(aq)
                           $\longrightarrow$ Fe(OH)_3(s)+ 3 NH₄⁺_(aq)+ 3Cl^–_(aq)
Fe³⁺_(aq)+ 3OH^–_(aq) $\longrightarrow$ Fe(OH)_3(s)

d) K₂CrO_4(aq)+ Pb(NO₃)_2(aq) $\longrightarrow$ PbCrO_4(s)+ 2KNO_3(aq)
2K⁺_(aq)+ CrO₄^2-_(aq)+ Pb²⁺_(aq)+ 2NO₃^–_(aq)
                           $\longrightarrow$ PbCrO_4(s)+ 2K⁺_(aq)+ 2NO₃^–_(aq)
CrO₄^2-_(aq)+ Pb²⁺_(aq) $\longrightarrow$ PbCrO_4(s)

e) KClO_3(aq)+ MgCl_2(aq) $\longrightarrow$ N.R.

f) (NH₄)₂CO_3(aq)+ CaCl_2(aq) $\longrightarrow$ CaCO_3(s)+ 2NH₄Cl_(aq)
2NH₄⁺_(aq)+ CO₃^2-_(aq)+ Ca²⁺_(aq)+ 2Cl^–_(aq)
                           $\longrightarrow$ CaCO_3(s)+ 2NH₄⁺_(aq)+ 2Cl^–_(aq)
CO₃^2-_(aq)+ Ca²⁺_(aq) $\longrightarrow$ CaCO_3(s)

g) NaC₂H₃O_2(aq)+ BaCl_2(aq) $\longrightarrow$ N.R.

21.  a) redox      b) acid-base           c) redox
d) acid-base       e) precipitation      f) precipitation

22.  a) decomposition, which is a type of redox

b) single-replacement, which is a type of redox

c) single-replacement, which is a type of redox

d) precipitation, which is a type of double replacement (but not redox!)

e) composition (sometimes also called a combination reaction or a synthesis reaction), which is a type of redox

f) acid-base, which is a type of double replacement (but not redox!)