Chapter 6. Chemical Reactions and Equations

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:

4 Na(s) + 2 Cl2(g) [latex]\longrightarrow[/latex] 4 NaCl(s)

4. Does the following chemical reaction proceed as written? Why or why not?

3 Zn(s) + 2 Al(NO3)3(aq) [latex]\longrightarrow[/latex] 3 Zn(NO3)2(aq) + 2 Al(s)

5. Explain what is wrong with this double-replacement reaction.

NaCl(aq) + KBr(aq) [latex]\longrightarrow[/latex] NaK(aq) + ClBr(aq)

6. Predict the products of and balance this double-replacement reaction.

Ag2SO4(aq) + SrCl2(aq) [latex]\longrightarrow[/latex] ?

7. Write the complete and net ionic equations for this double-replacement reaction.

BaCl2(aq) + Ag2SO4(aq) [latex]\longrightarrow[/latex] ?

8. Write the complete and net ionic equations for this double-replacement reaction.

Ag2SO4(aq) + SrCl2(aq) [latex]\longrightarrow[/latex] ?

9. Identify the spectator ions in this reaction. What is the net ionic equation?

NaCl(aq) + KBr(aq) [latex]\longrightarrow[/latex] NaBr(aq) + KCl(aq)

10. Can a reaction be a composition reaction and a redox reaction at the same time? Give an example to support your answer.

11. Can a reaction be a decomposition reaction and a redox reaction at the same time? Give an example to support your answer.

12. Why is CH4 not normally considered an acid?

13. What are the oxidation numbers of the nitrogen atoms in these substances?

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

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

14.  Disproportion is a type of redox reaction in which the same substance is both oxidized and reduced. Identify the element that is disproportionating and indicate the initial and final oxidation numbers of that element.

2 CuCl(aq) [latex]\longrightarrow[/latex] CuCl2(aq) + Cu(s)

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  [latex]\longrightarrow[/latex]  zinc sulfate + hydrogen

b) carbon + oxygen  [latex]\longrightarrow[/latex]  carbon dioxide

c) hydrogen + oxygen  [latex]\longrightarrow[/latex]  water

d)  aluminum + hydrochloric acid  [latex]\longrightarrow[/latex] aluminum chloride + hydrogen

e) chromium + oxygen  [latex]\longrightarrow[/latex] chromium(III) oxide

f) potassium + water  [latex]\longrightarrow[/latex]  potassium hydroxide + hydrogen

g) copper(II) oxide + hydrochloric acid [latex]\longrightarrow[/latex]  copper(II) chloride + water 

h) sodium hydrogen carbonate + nitric acid [latex]\longrightarrow[/latex]  sodium nitrate + water + carbon dioxide

17. Balance the following equations:

a) H3PO4  +  CaO [latex]\longrightarrow[/latex] Ca3(PO4)2  +  H2O                    

b) NH3  +  O2 [latex]\longrightarrow[/latex] NO2  +  H2O

c) Cl2O7  +  H2O [latex]\longrightarrow[/latex] HClO4                                       

d) Mg3N2  +  H2O [latex]\longrightarrow[/latex] Mg(OH)2  +  NH3

e) FeSO4 [latex]\longrightarrow[/latex] Fe2O3  +  SO2  +  O2                             

f)P4  +  Cl2 [latex]\longrightarrow[/latex] PCl3

g) MnO2  +  C [latex]\longrightarrow[/latex] Mn  +  CO2                                     

h) Na2O2  +  H2O [latex]\longrightarrow[/latex] NaOH   +  O2

i) CaH2  +  H2O [latex]\longrightarrow[/latex] Ca(OH)2  +  H2                             

j)NaHCO3 [latex]\longrightarrow[/latex] Na2CO3  +  CO2  +  H2O

18. Balance the following equations:

a)  Mg  +  O2  [latex]\longrightarrow[/latex] MgO                                          

b)  KClO3  [latex]\longrightarrow[/latex] KCl  +  O2

c)  Fe  +  O2  [latex]\longrightarrow[/latex] Fe3O4                                         

d)  Mg +  HCl  [latex]\longrightarrow[/latex] MgCl2  +  H2

e)  Na  +  H2O  [latex]\longrightarrow[/latex] NaOH  +  H2                            

f)  N2+  H2 [latex]\longrightarrow[/latex] NH3

g)  Na2CO3•10H2O   [latex]\longrightarrow[/latex]  Na2CO3+  H2O               

h)  Fe +  H2O  [latex]\longrightarrow[/latex] Fe3O4+  H2

i)  F2  +  H2O  [latex]\longrightarrow[/latex] HF +  O2

19. Balance the following chemical equations.

a)   Ca3(PO4)2   +   SiO2   +   C   [latex]\longrightarrow[/latex]    P4  +    CaSiO3    +   CO2

b)   C2H6O2   +   O3  [latex]\longrightarrow[/latex]    CO2   +   H2O

c)   Fe3O4    +    S8   [latex]\longrightarrow[/latex]  Fe2S3   +    SO3

d)   P2S5   +    O2   [latex]\longrightarrow[/latex] S8   +    P3O8

e)   C3H8   +    SO2 [latex]\longrightarrow[/latex] 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) [latex]\longrightarrow[/latex]                        

b)  BaCl2(aq)  +  H2SO4(aq) [latex]\longrightarrow[/latex]

c)  FeCl3(aq)  +  NH4OH(aq) [latex]\longrightarrow[/latex]                       

d)  K2CrO4(aq)  + Pb(NO3)2(aq) [latex]\longrightarrow[/latex]

e)  KClO3(aq)  +  MgCl2(aq) [latex]\longrightarrow[/latex]                        

f)  (NH4)2CO3(aq)  +  CaCl2(aq) [latex]\longrightarrow[/latex]

g)  NaC2H3O2(aq)  +  BaCl2(aq) [latex]\longrightarrow[/latex]

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)+ H2SO4(aq) [latex]\longrightarrow[/latex] Fe3(SO4)2(aq)+ H2(g)

b)  HClO4(aq)+ RbOH(aq) [latex]\longrightarrow[/latex] RbClO4(aq)+ H2O(l)

c)  Ca(s)+ O2(g) [latex]\longrightarrow[/latex] CaO(s)

d)  H2SO4(aq)+ NaOH(aq) [latex]\longrightarrow[/latex] Na2SO4(aq)+ H2O(l)

e)  Pb(NO3)2(aq)+ Na2CO3(aq) [latex]\longrightarrow[/latex] PbCO3(s)+ NaNO3(aq)

f)  K2SO4(aq)+ CaCl2(aq) [latex]\longrightarrow[/latex] KCl(aq)+ CaSO4(s)

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

a)  I4O9(s) [latex]\longrightarrow[/latex] I2O6(s)+ I2(s)+ O2(g)

b)  Mg(s)+ AgNO3(aq) [latex]\longrightarrow[/latex] Mg(NO3)2(aq)+ Ag(s)

c)  SiCl4(l)+ Mg(s) [latex]\longrightarrow[/latex] MgCl2(aq)+ Si(s)

d)  CuCl2(aq)+ AgNO3(aq) [latex]\longrightarrow[/latex] Cu(NO3)2(aq)+ AgCl(s)

e)  Al(s)+ Br2(l) [latex]\longrightarrow[/latex] AlBr3(s)

f)  HBr(aq)+ NaOH(aq) [latex]\longrightarrow[/latex] NaBr(aq)+ H2O(l)

Answers

1. H2O(ℓ) [latex]\longrightarrow[/latex] H2O(g)

2. H2O(ℓ) [latex]\longrightarrow[/latex] 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) [latex]\longrightarrow[/latex] SrSO4(s) + 2 AgCl(s) 

7. Complete ionic equation: Ba2+(aq) + 2 Cl−(aq) + 2 Ag+(aq) + SO42−(aq) [latex]\longrightarrow[/latex] 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) [latex]\longrightarrow[/latex] 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 [latex]\longrightarrow[/latex] 2 HCl (answers will vary)

11. Yes; 2 HCl [latex]\longrightarrow[/latex] 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) [latex]\longrightarrow[/latex] Hg(l) + O2(g)
b)  Zn(s) + HCl(aq) [latex]\longrightarrow[/latex] ZnCl2(aq) + H2(g)
c)  C3H8(g) + O2(g) [latex]\longrightarrow[/latex] CO2(g) + H2O(g)
d)  NH3(g) + HNO3(aq) [latex]\longrightarrow[/latex] NH4NO3(s)
e)  B2O3(s) + Mg(s) [latex]\longrightarrow[/latex] B(s) + MgO(s)

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

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

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

19. Balance the following chemical equations.

a)  2 Ca3(PO4)2+  6 SiO2+  5 C  [latex]\longrightarrow[/latex] P4+ 6 CaSiO3+ 5 CO2

b)  3 C2H6O2   +   5 O3   [latex]\longrightarrow[/latex]   6 CO2   +   9 H2O

c)  48 Fe3O4   +   35 S8  [latex]\longrightarrow[/latex]   72 Fe2S3   +   64 SO3

d)  24 P2S5   +  64O2 [latex]\longrightarrow[/latex] 15 S8   +   16 P3O8

e)  16 C3H8  +   56 SO2 [latex]\longrightarrow[/latex]  24 C2H4O4  +  16 H2O  +  7 S8

20.  a) NaCl(aq)+ AgNO3(aq) [latex]\longrightarrow[/latex] AgCl(s)+ NaNO3(aq)
Na+(aq)+ Cl–(aq)+ Ag+(aq)+ NO3–(aq)
                           [latex]\longrightarrow[/latex] AgCl(s)+ Na+(aq)+ NO3–(aq)
Cl–(aq)+ Ag+(aq) [latex]\longrightarrow[/latex] AgCl(s)

b) BaCl2(aq)+ H2SO4(aq) [latex]\longrightarrow[/latex] BaSO4(s)+ 2HCl(aq)
Ba2+(aq)+ 2Cl–(aq)+ 2H+(aq)+ SO42-(aq)
                           [latex]\longrightarrow[/latex] BaSO4(s)+ 2H+(aq)+ 2Cl–(aq)
Ba2+(aq)+ SO42-(aq) [latex]\longrightarrow[/latex] BaSO4(s)

c) FeCl3(aq)+ 3NH4OH(aq) [latex]\longrightarrow[/latex] Fe(OH)3(s)+ 3NH4Cl(aq)
Fe3+(aq)+ 3Cl–(aq)+ 3 NH4+(aq)+ 3OH–(aq)
                           [latex]\longrightarrow[/latex] Fe(OH)3(s)+ 3 NH4+(aq)+ 3Cl–(aq)
Fe3+(aq)+ 3OH–(aq) [latex]\longrightarrow[/latex] Fe(OH)3(s)

d) K2CrO4(aq)+ Pb(NO3)2(aq) [latex]\longrightarrow[/latex] PbCrO4(s)+ 2KNO3(aq)
2K+(aq)+ CrO42-(aq)+ Pb2+(aq)+ 2NO3–(aq)
                           [latex]\longrightarrow[/latex] PbCrO4(s)+ 2K+(aq)+ 2NO3–(aq)
CrO42-(aq)+ Pb2+(aq) [latex]\longrightarrow[/latex] PbCrO4(s)

e) KClO3(aq)+ MgCl2(aq) [latex]\longrightarrow[/latex] N.R.

f) (NH4)2CO3(aq)+ CaCl2(aq) [latex]\longrightarrow[/latex] CaCO3(s)+ 2NH4Cl(aq)
2NH4+(aq)+ CO32-(aq)+ Ca2+(aq)+ 2Cl–(aq)
                           [latex]\longrightarrow[/latex] CaCO3(s)+ 2NH4+(aq)+ 2Cl–(aq)
CO32-(aq)+ Ca2+(aq) [latex]\longrightarrow[/latex] CaCO3(s)

g) NaC2H3O2(aq)+ BaCl2(aq) [latex]\longrightarrow[/latex] 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!)

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