Chemistry 12
Equilibrium Problems #3
1. Consider the following equilibrium reaction:
H2(g) + Br2(g) < === > 2HBr(g) + energy
The Keq for this reaction at 25oC is 1.22. At equilibrium, the concentration of HBr is 0.50M.
Assuming H2 and Br2 are present at equal amounts, calculate the concentration of H2 at
equilibrium.
(0.23M)
2. For the reaction:
N2(g) + 3H2(g) < === > 2NH3(g) + 92 kJ
at an equilibrium temperature of 1000oC, a 1.00 L flask contains 0.102 mol of ammonia. 1.03 mol
of nitrogen, and 1.62 mol of hydrogen. Calculate the equilibrium constant at this temperature.
(Keq=2.38x10-6)
3. For the following reaction at equilibrium at 2000 oC, the concentration of N2 and O2 are both 5.2
M.
N2(g) + O2(g) < === > 2NO(g)
Keq = 6.2x10-4
Calculate the concentrations of NO.
(0.13M)
4. In the following reaction at equilibrium at 2000 oC,
Keq= 1.6x103
2NO(g) < === > N2(g) + O2(g)
The concentration of NO is 0.13M. If the concentration of N 2 and O2 are equal, calculate the
concentration of N2.
(5.3M)
5. At equilibrium at 1120oC, the concentrations of the reactants and products are measured and
found to be [CO]=0.010M, [H2O]=0.020M, [CO2]=0.010M, and [H2]=0.010M. For the following
reaction, does the equilibrium favour the formation of the products or the reactants?
CO(g) + H2O(g) < === > CO2(g) + H2(g)
6. A 1.00L reaction container initially contains 9.28x10 -3 mol of H2S only. At equilibrium the
concentration of H2S is 7.06x10-3M. Calculate the equilibrium constant for this reaction.
H2S(g) < === > 2H2(g) + S2(g)
(Keq=6.03x10-6)
7. The equilibrium constant for the decomposition of phosphorus pentachloride to form
phosphorus trichloride gas and chlorine gas is 0.0211 at a certain temperature. If he initial
concentration of PCl5 is 1.00M, what is the equilibrium concentration of chlorine?
(0.135M)
8. At 35oC, K=1.6x10-5 for the reaction:
2NOCl(g) < === > 2NO(g) + Cl2(g)
Calculate the concentration of all species at equilibrium if 2.0 mol of pure NOCl (g) is initially
added to a 2.0 L flask.
(0.97M, 0.032M, 0.016M)
9. At a particular temperature, assume that K=1.0 x 10 2 for the reaction:
H2(g) + F2(g) < ==== > 2HF(g)
In an experiment, 2.0 mol of H2 and 2.0 mol F2 are introduced to 1.0 L flask. Calculate the
concentrations of H2 at equilibrium.
(0.33M)
10. At 90.0oC, the equilibrium constant is 6.8 x 10-2 for the reaction:
H2(g) + S(s) < === > H2S(g)
If 0.15 mol hydrogen and 1.0 mol sulphur are heated to 90.0 oC in a 1.0 L container, what will be
the concentration of H2S at equilibrium?
(9.6x10-3M)
11. Consider the following equilibrium:
CH4(g) + H2O(g) < ==> CO(g) + 3H2(g)
Keq
1.74x10-3
4.68x10-2
Temperature
800oC
1000oC
Is the forward reaction in this equilibrium exothermic or endothermic? Explain your answer.
12. Consider the following equilibrium:
CO(g) + Cl2(g) < === > COCl2(g)
At equilibrium, the system contains 2.00 mol CO, 1.00 mol Cl 2 and 0.200 mol COCl2 in a 2.0 L
container. Calculate the Keq.
(0.200)
13. Consider the following:
H2(g) + Br2(g) < === > 2HBr(g)
Keq=12.0
Initially, 0.080 mol H2 and 0.080 mol Br2 are placed into a 4.00 L container. What is the [HBr] at
equilibrium?
(0.025M)
14. Consider the following:
N2O4(g) < === > 2NO2(g) Keq=9.5 x10-3
Initially, 0.060 mol N2O4 and 0.020 mol NO2 are placed into 2.00L container. Use calculations to
determine the direction in which the reaction proceeds in order to reach equilibrium.
15. In the equilibrium
H2(g) + I2(g) < === > 2 HI(g)
Keq = 62 under certain conditions. If the initial concentrations were [H2]=1.00 M, [I2]= 2.00 M,
and [HI]=0 M. What were the equilibrium concentrations?
(0.055M, 1.1M, 1.9M)
16. At a certain temperature the Keq for the reaction 2HF < === > H2 (g) + F2 (g). Find the
equilibrium concentrations if the following systems are introduced into a 5.0L bulb.
a)
b)
c)
3.0 mol of HF, 2.0 mol of H2 and 4.0mol of F2
0.20 mol of HF, 0.50 mol of H2 and 0.60mol of F2
0.30 mol of HF, 1.8 mol of H2 and 0.20mol of F2
17. A reaction mixture for CO(g) + H2O(g) < === > H2 (g) + CO2 (g) contains 1.00 mol of H2,
2.00 mol of CO2 , 2.00mol of CO and 2.00 mol of H2O. If 1.00 mol of H2 is added calculate the
equilibrium concentration of CO. (1.17M)