Homework – Ch 17 and 18
1. Suppose a thin sheet of zinc containing 0.2 moles of the metal is completely converted to zinc oxide (ZnO) in one
month. How would you express the rate of conversion of the zinc?
2. a. What is collision theory?
b. According to this theory, what two conditions must be met in order for a collision between reactant
molecules to be effective in producing new chemical species?
c. Does every collision between reacting particles lead to products? Explain.
3. Refrigerated food stays fresh for long periods. The same food stored at room temperature quickly spoils. Why?
4. How is the equilibrium position of this reaction affected by the following changes?
C(s) + H2O(g) + heat
CO(g) + H2(g)
a. Lowering the temperature
b. Increasing the pressure
c. Removing hydrogen
d. Adding water vapor
5. The reversible reaction N2(g) + 3H2(g)
2NH3 (g) produces ammonia, which is a fertilizer. At equilibrium, a
1-L flask contains 0.15 mol H2, 0.25 mol N2, and 0.10 mol of NH3. Calculate Keq for the reaction.
6. What are three stresses that can upset the equilibrium of a chemical system?
7. What does the value of the equilibrium constant tell you about the amounts of reacants and products present at
equilibrium?
8. How do the amounts of reactants and products change after a reaction has reached chemical equilibrium?
9. How can a balanced chemical equation be used to write an equilibrium-constant expression?
10. Using the following equilibrium constants for several reactions, determine in which reactions the products are
favored. Why?
Keq = 1 x 102
b. Keq = 0.003
c. Keq = 3.5
11. Lead (II) sulfide (PbS) has a Ksp of 3.0 X 10 –28. What is the concentration of lead (II) ions in a saturated solution of
PbS?
12. What is the concentration of calcium ions in a saturated calcium carbonate solution at 25˚C? (Ksp = 4.5 X 10-9)
13. What is the concentration of sulfide ion in a 1.0 L solution of iron (II) sulfide to which 0.04 mol of iron(II)nitrate
is added? The Ksp of FeS is 8 X 10 –19.
14. Which compound, FeS (Ksp= 8.0 X 10 –19) or CuS (Ksp= 8.0 X 10-37), has the higher solubility?
15. What two factors determine the spontaneity of a reaction?
16. What is the sign (+ or -) of the Gibbs free-energy change in a spontaneous process?
17. Suppose the products in a spontaneous process are more ordered than the reactants. Is the entropy change
favorable or unfavorable?
18. Explain why, under certain circumstances, a nonspontaneous reaction becomes spontaneous?
19. A considerable amount of heat is required for the decomposition of aluminum oxide.
2Al2O3(s)  4Al(s) + 3O2(g)
ΔH= 3352 kJ
a. What is the enthalpy change for the formation of 1 mol of aluminum oxide from its elements?
b. Is the reaction exothermic or endothermic?
20. Calculate the enthalpy change for the formation of lead(IV) chloride by the reaction of lead (II) chloride with
chlorine.
PbCl2 (s) + Cl2 (g)  PbCl4(l)
ΔH=?
Use the following thermochemical equations.
Pb(s) + 2Cl2(g)  PbCl4(l)
ΔH= -329.2 kJ
Pb(s) + Cl2(g)  PbCl2 (s)
ΔH= -359.4 kJ
21. Find the enthalpy change for the formation of phosphorus pentachloride from its elements.
2P(s) + 5Cl2 (g)  2PCl5 (s)
Use the following thermochemical equations.
PCl5 (s)  PCl3 (g) + Cl2 (g)
ΔH= 87.9 kJ
2P(s) + 3 Cl2 (g)  2PCl3 (g)
ΔH= - 574kJ
22. Use standard heats of formation (ΔHf0) to calculate the change in enthalpy for these reactions.
a. 2C(s,graphite) + O2 (g)  2CO(g)
b. 2H2O2 (l)  2H2O(l) + O2 (g)
c. 4NH3(g) + 5O2(g)  4NO(g) + 6H2O(g)
23. Calculate the enthalpy change (ΔH) for the formation of nitrogen monoxide from its elements.
N2(g) + O2 (g)  2NO(g)
Use these thermochemical equations:
4NH3 (g) + 3O2 (g)  2N2 (g) + 6H2O (l)
ΔH= -1.53 X 103 kJ
4NH3(g) + 5O2 (g)  4NO(g) + 6H2O (l)
ΔH= -1.17 X 103 kJ