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Ch. 15 Kimball Spring 2019
Discussion Worksheet - Chapter 15
Chemical Equilibrium – Part 2
Dr Cabirac Lecture
1. Consider the following equilibrium process at 686ºC:
CO2 (g) + H2 (g) ⇋ CO(g) + H2O (g)
The equilibrium concentrations of the reacting species are [CO] = 0.050 M, [H2] = 0.045 M,
[CO2] = 0.086 M, and [H2O] = 0.040 M.
A. Calculate Kc for the reaction at 686ºC.
Kc = 0.517
B. If we add CO2 to increase its concentration to 0.50 mol/L, what will be the concentrations of all
the gases when equilibrium is reestablished?
[CO2] = 0.475 M
[H2] = 0.020 M
[CO] = 0.025 M
[H2O] = 0.015 M
2. At 1000 K, a sample of pure NO2 gas decomposes:
2NO2 (g) ⇋ 2NO (g) + O2 (g)
The equilibrium constant Kp is 158. Analysis shows that the partial pressure of O2 is 0.25 atm at
equilibrium. Calculate the pressure of NO and NO2 in the mixture.
𝑷𝑵𝑶 = 𝟎. 𝟓𝟎 𝑴
𝑷𝑵𝑶𝟐= 𝟎. 𝟎𝟐𝟎 𝑴
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Ch. 15 Kimball Spring 2019
3. Consider the equilibrium 2NOBr (g) ⇋ 2NO (g) + Br2 (g)
If nitrosyl bromide (NOBr) is 34% dissociated at 25ºC and the total pressure is 0.25 atm, calculate Kp and
Kc at this temperature.
Kp = 9.3 x 10-3
Kc = 4.0 x 10-5
4. For the synthesis of ammonia: N2 (g) + 3H2 (g) ⇋ 2NH3 (g)
The equilibrium constant Kc at 375ºC is 1.2. Starting with [H2]0 = 0.76 M, [N2]0 = 0.60 M, and [NH3]0 =
0.48 M, which gases will have increased in concentration and which will have decreased in concentration
when the mixture comes to equilibrium?
Kc > Qc , so rxn will shift → to achieve equilibrium
[N2], [H2] decrease
[NH3] increase
5. A mixture of 0.500 mol H2 and 0.500 mol I2 was placed in a 1.00 L flask at 430ºC. The equilibrium
constant Kc for the reaction H2 (g) + I2 (g) ⇋ 2HI(g)
is 54.3 at this temperature.
Calculate the concentrations of H2 , I2 , and HI at equilibrium.
[H2] = 0.107 M
[I2] = 0.107M
[HI] = 0.785 M
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Ch. 15 Kimball Spring 2019
6. Consider the following equilibrium: H2O (g) + C(s) ⇋ CO(g) + H2 (g) ∆H = +131.3 kJ
In which direction would the equilibrium shift if:
A. H2O were added to the system →
B. C were added to the system no change
C. CO were added to the system ←
D. H2 were removed from the system →
E. Pressure were increased ←
F. Volume were doubled →
G. Temperature were increased →
7. For the following reaction at 100 ◦C Kc = 16
H2(g) + Br2(g) 2HBr(g)
At the start of the reaction 0.80 mol of H2, 0.80 mol of Br2, and 8.0 moles of HBr are introduced into a
1.00 L reaction vessel and allowed to come to equilibrium. Calculate [HBr] at equilibrium.
[HBr] = 6.4 M
8. Based on the data from the graph below, what is the value of the equilibrium constant, K, for the
conversion of reactant A to product B.
Kc = 4.7
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