Equilibrium Problems from Masterton
1. Write the equilibrium constant expression for
a. 2 SO2(g) + O2(g)  2 SO3(g)
b. 2 O2(g) + 2 H2S(g)  2 H2O (g) + 2 SO2(g)
c. 2 NO2(g) + 7 H2(g)  2 NH3(g) + 2 H2O(g)
2. Write the Kc expression for
a. Fe(s) + 5 CO2(g)  Fe(CO)5(g)
b. 6 F2(g) + 2 NH3(g)  2 NF3(g) + 6 HF(g)
c. Mg3N2(s) + 6 H2O(g)  3 Mg(OH)2(s) + 2 NH3(g)
d. 3 Mg(OH)2(s) + 2 NH3(g)  Mg3N2(s) + 6 H2O(l)
3. Write a chemical equation for an equilibrium system that would lead to each of
the following expressions for Kc.
a. [H2]2 x [S2]
b.
[HI]2_______
2
[H2S]
[H2] x [I2]
4. Given
2 CO2 (g)  2 CO(g) + O2(g) Kc = 26
N2(g) + 3 H2(g)  2NH3(g) Kc = 2 x 10-5
Determine the equilibrium constant at the same temperature for
a. CO2(g)  CO(g) + ½ O2(g)
b. 2 NH3 (g)  N2(g) + 3 H2(g)
5. Calculate the Kc at 1500°C for
2NO(g)  N2(g) + O2(g)
given that the equilibrium concentrations of N2, O2 and NO are 0.040 M, 0.040 M
and 0.00035 M respectively.
6. For the reaction in Problem 5 at a different temperature, if one starts with pure
NO at 4.00 M, the equilibrium concentrations of N2 and O2 are each 1.28 M.
Calculate the Kc at this temperature.
7. When 1.36 mol H2 and 0.78 mol CO are put in a one-liter sealed container at
160C, the following equilibrium is established:
CO(g) + 2 H2(g)  CH3OH(g)
The equilibrium concentration of H2 is 0.120 mol/L. Calculate
a. [CO]
b. [CH3OH]
c. Kc
8. Kc is 0.56 at 300°C for the system: PCl5(g)  PCl3(g) + Cl2(g)
In a 5.0 L flask, a gaseous mixture consists of 0.45 mol Cl2, 0.90 mol PCl3, and 0.12
mol PCl5.
a. Is the mixture at equilibrium? Explain.
b. If not at equilibrium, which way will the system shift to establish
equilibrium?
9. At a certain temperature, Kc is 16 for the reaction
2 SO2(g) + O2 (g)  2SO3(g)
Predict in which direction the system will move to reach equilibrium if we start with
a. 0.850 mol SO3 in a 3.0L container
b. a gaseous mixture of 0.24 mol SO2, 0.40 mol O2 and 0.60 mol SO3 in a 4.0L
container
10. Kc for the reaction - 2ICl(g)  I2(g) + Cl2(g) is 0.11 at a certain
temperature. Suppose the initial concentrations of ICl, I2 and Cl2 are 0.20 M. 0.00M
and 0.00M, respectively. Some of the ICl decomposes and the system reaches
equilibrium. What is the equilibrium concentration of each species?
11. The reaction – CO(g) + H2O(g)  CO2(g) + H2(g) has a Kc value of 4.0 at
500°C. Calculate the concentration of all species at equilibrium with
a. [CO]=[H2O] = 0.100M
b. [CO]=[H2O]=[CO2]=[H2] = 0.040M
12. For the system – SnO2(s) + 2 H2(g)  Sn(s) + 2 H2O(g) at 500°C, [H2O] =
[H2] = 0.10M.
a. Calculate the Kc at this temperature.
b. Enough H2 is added to raise its concentration temporarily to 0.18 M.
When equilibrium is restored, what are the concentrations of H2O and H2?
13. Consider the system – 2H2S(g) + 3 O2(g)  2 H2O(g) + 2 SO2(g)
H for the forward reaction is -1036kJ. Predict whether the forward or reverse
reaction will occur when the equilibrium is disturbed by
a. expanding the container at constant temperature
b. removing SO2
c. raising the temperature
d. absorbing the water vapor
14. Predict the direction in which each of the following equilibria will shift if the
pressure on the system is increased by compression (how does that impact
volume?)
a. ClF5(g)  ClF3(g) + F2(g)
b. H2O(g) + C(s)  CO(g) + H2(g)
c. HBr(g)  ½ H2(g) + ½ Br2(g)
15. For the system - 2P(s) + 3H2(g)  2PH3(g)
Kc is 3.6 x 10-4 at 227°C and 2.3 x 10-3 at 477°C. Is the forward reaction exothermic
or endothermic? Explain.
16. Given the following Kp values at 25°C,
NH4Cl(s)  NH3(g) + HCl(g) Kp = 7.7 x 10-17
2 NO2(g)  2 NO(g) + O2(g)
Kp = 6.1 x 10-13
H2(g) + I2(g)  2 HI(g)
Kp = 8.7 x 102
Calculate the corresponding values of Kc.