Chapter 15 – Chemical Equilibrium
SELF TEST QUESTIONS
1. Write the equilibrium expression for each of the following reactions:
a. 2H2 (g) + O2 (g) ↔ 2H2O (g)
b. Cl2 (g) + 2Fe2+(aq) ↔ 2Fe3+ (aq) + 2Cl- (aq)
c. Cu2+ (aq) + 4NH3 (aq) ↔ Cu (NH3)42+ (aq)
2. Write the equilibrium expression for each of the following reactions:
a. 2NO (g) + O2 (g) ↔ 2NO2 (g)
b. Ag+ (aq) + I- (aq) ↔ AgI(s)
c. Fe3+ (aq) + 3OH-(aq) ↔ Fe (OH)3 (s)
3. Write the equilibrium expression for each of the following reactions:
a. Zn2Fe (CN)6 (s) ↔ 2Zn2+ (aq) + Fe (CN)64b. H+(aq) + OH-(aq) ↔ H2O (l)
4. Calculate the equilibrium constant, Kp at 25oC for the reaction:
2NO (g) + O2 (g) ↔ 2NO2 (g)
If the equilibrium pressures are NO2 = 0.55 atm, NO = 6.5 x 10-5 atm, O2 = 4.5 x 10-5 atm.
5. Calculate the equilibrium constant, K, at 25oC for the Haber process:
3H2 (g) + N2 (g) ↔ 2NH3 (g)
If the equilibrium concentrations are [H2] = 0.85 M, [N2] = 1.33 M, [NH3] = 0.22 M.
6. Given your answer from problem #4, calculate the value for Kp at 25oC for each of the
following reactions:
a. 1/2 NO(g) + 1/4 O2(g) ↔ 1/2 NO2 (g)
b. 2NO2 (g) ↔ 2NO (g) + O2 (g)
c. NO2 (g) ↔ NO(g) + 1/2 O2 (g)
7. Given your answer from problem #5, calculate the value for K at 25oC for each of the
following reactions:
a. 2NH3 (g) ↔ 3H2 (g) + N2 (g)
b. NH3 (g) ↔ 3/2 H2 (g) + 1/2 N2 (g)
c. 6NH3 (g) ↔ 9H2 (g) + 3N2 (g)
8. The dissociation of acetic acid, CH3COOH, has an equilibrium constant at 25oC
of 1.8 x 10-5. The reaction is:
CH3COOH (aq) ↔ CH3COO-(aq) + H+(aq)
If the equilibrium concentration of CH3COOH is 0.46 moles in 0.500 L of water and that
of CH3COO- is 8.1 x 10-3 moles in that same 0.500 L, calculate [H+] for the reaction.
Chapter 15 – Chemical Equilibrium
9. Write the chemical equation for the reaction in problem #8 if the value of
K is 5.6 X 104 (1/Koriginal).
10. Derive an expression that relates K to Kp, and calculate the value of K at 25oC, for the
reaction given in problem #4.
11. Calculate the value for Kp at 25oC if the value for K is 3.7 x 109 mol- for the reaction
CO (g) + Cl2 (g) ↔ COCl2 (g)
12. The reaction of methane with water is given by the following equation:
CH4 (g) + H2O (g) ↔ CO(g) + 3H2 (g)
K = 5.67
Predict the direction that the system will shift in order to reach equilibrium given the
following initial values of Q.
a. Q = 11.85
b. Q = 3.8 x 10-4
c. Q = 5.67
13. Using the same reaction as in problem #12, determine the direction that the system
will shift in order to reach equilibrium given the following initial concentrations.
[CH4]
a. 0.500
b. 4.6x10-3
c. 0.818
[H2O]
0.300
0.800
0.750
[CO]
0.620
0.200
0.650
[H2]
0.100
1.00
2.00
14. The reaction,
2NO (g) ↔ N2 (g) + O2 (g)
has a value of K = 2.4 x 103 at 2000 K. If 0.61 g of NO are put in a previously 3.00 L
vessel, calculate the equilibrium concentrations of NO, N2, and O2.
15. Using the same reaction at 2000 K as in problem #14, calculate the equilibrium
concentrations of NO, N2, and O2 if the initial concentrations of each species are [NO]= 0,
[N2] = 0.850 M, and [O2] = 0.560 M.
16. Hypobromous acid, HOBr, dissociates in water according to the following reaction:
HOBr (aq) ↔ OBr - (aq) + H+(aq)
K = 2.06 x 10-9 at 25oC
+
Calculate [H ] of a solution originally 1.25 M in HOBr.
17. Ammonia undergoes hydrolyses according to the following reaction:
NH3 (aq) + H2O(l) ↔ NH4 (aq) + OH-(aq)
K = 1.8 x 10-5 at 25oC
Calculate [NH3], [NH4+], and [OH-] in a solution originally 0.200 M in NH3.
18. Using the same reaction and value for K as in problem #17, determine [OH-] if
[NH3]= 0.500 M and [NH4+] = 0.750 M.
Chapter 15 – Chemical Equilibrium
19. The equilibrium constant for the reaction:
SbCl3(g) + Cl2 (g) ↔ SbCl5 (g)
At 448oC is 40. What are the equilibrium concentrations of SbCl3, Cl2, and SbCl5 if
[Cl2]o= 0.620 M and [SbCl5]o = 0.180 M?
20. Using the same reaction an K as in problem #19, calculate the equilibrium
concentrations of all species if [SbCl5]o = 1.25 M and [Cl2]o = [SbCl3]o = 0.
21. The reaction of carbon disulfide with chlorine is as follows:
CS2 (g) + 3Cl2 (g) ↔ CCl4 (g) + S2Cl2 (g)
∆Ho = -238 kJ
Predict the effect of each of the following changes to the system on the direction of
equilibrium:
a. The pressure on the system is double by halving the volume.
b. Chlorine is removed as it is generated.
c. Heat is added to the system.
22. The reaction of nitrogen gas with hydrogen chloride is as follows:
N2 (g) + 6HCl(g) ↔ 2NH3 (g) + 3Cl2 (g)
∆H = 461 kJ
Predict the effect of each of the following changes to the system on the direction of
equilibrium:
a. Triple the volume of the system.
b. The amount of nitrogen in doubled.
c. Heat is added to the system.