12) The equilibrium constant (Kp) for the interconversion of PCl5 and PCl3 is 0.0121:
PCl5 (g) PCl3 (g) + Cl2 (g)
A vessel is charged with PCl5 giving an initial pressure of 0.123 atm. At equilibrium, the partial pressure
of PCl3 is ________ atm.
A) 0.0782
B) 0.0455
C) 0.0908
D) 0.0330
E) 0.123
13) At 200 °C, the equilibrium constant (Kp) for the reaction below is 2.40 × 103.
2NO (g) N2 (g) + O2 (g)
A closed vessel is charged with 36.1 atm of NO. At equilibrium, the partial pressure of O2 is ________
atm.
A) 294
B) 35.7
C) 17.9
D) 6.00
E) 1.50 × 10-2
15.3 Algorithmic Questions
1) Which of the following expressions is the correct equilibrium-constant expression for the equilibrium
between dinitrogen tetroxide and nitrogen dioxide?
5N2O4(g) 10NO2 (g)
A) [NO2]10/[N2O4]5
B) [N2O4]10/[NO2]5
C) [NO2]5/[N2O4]10
D) [NO2]5/[N2O4]5
E) [N2O4]5/[NO2]5
2) Given the following reaction at equilibrium, if Kc = 5.84 x 105 at 230.0 °C, Kp = ________.
2NO (g) + O2 (g) 2NO2 (g)
A) 3.67 × 10-2
B) 1.41 × 104
C) 6.44 × 105
D) 2.40 × 106
E) 2.41 × 107
3) Given the following reaction at equilibrium at 450.0 °C:
CaCO3 (s) CaO (s) + CO2 (g)
If pCO2 = 0.0155 atm, Kc = ________.
A) 155
B) 0.0821
C) 0.920
D) 2.61 × 10-4
E) 9.20
4) Given the following reaction at equilibrium, if Kp = 1.10 at 250.0 °C, Kc = ________.
PCl5 (g) PCl3 (g) + Cl2 (g)
A) 3.90 × 10-6
B) 2.56 × 10-2
C) 1.10
D) 42.9
E) 47.2
5) Given the following reaction at equilibrium at 300.0 K:
NH4HS (s) NH3 (g) + H2S (g)
If pNH3 = pH2S = 0.105 atm, Kp = ________.
A) .0110
B) 4.99 × 10-4
C) .105
D) .0821
E) 5.66 × 10-3
6) The value of Keq for the following reaction is 0.25:
SO2 (g) + NO2 (g) SO3 (g) + NO (g)
The value of Keq at the same temperature for the reaction below is ________.
3SO2 (g) + 3NO2 (g) 3SO3 (g) + 3NO (g)
A) 1.6 × 10-2
B) 7.5 × 10-1
C) 8.3 × 10–2
D) 6.4 × 101
E) 0.25
7) The Keq for the equilibrium below is 7.52 × 10-2 at 480.0 °C.
2Cl2 (g) + 2H2O (g) 4HCl (g) + O2 (g)
What is the value of Keq at this temperature for the following reaction?
8HCl (g) + 2O2 (g) 4Cl2 (g) + 4H2O (g)
A) 1.77 × 102
B) 5.66 × 10-3
C) 1.50 × 10-1
D) -7.52 × 10-2
E) 7.52 × 10-2
8) The Keq for the equilibrium below is 5.4 × 1013 at 480.0 °C.
2NO (g) + O2 (g) 2NO2 (g)
What is the value of Keq at this temperature for the following reaction?
4NO (g) + 2O2 (g) 4NO2 (g)
A) 2.9 × 1027
B) 8.5 × 1054
C) 3.4 × 10–28
D) -1.1 × 1014
E) 5.4 × 1013
9) The Keq for the equilibrium below is 0.112 at 700.0 °C.
SO2 (g) + O2 (g) SO3 (g)
What is the value of Keq at this temperature for the following reaction?
2SO2 (g) + O2 (g) 2SO3 (g)
A) 1.25 × 10-2
B) 2.24 × 10-1
C) 7.97 × 101
D) 4.46
E) 0.112
10) The value of Keq for the following reaction is 0.26:
A (g) + B (g) C (g) + D (g)
The value of Keq at the same temperature for the reaction below is ________.
2A (g) + 2B (g) 2C (g) + 2D (g)
A) 0.068
B) 0.52
C) 1.2
D) 0.065
E) 0.26
11) The value of Keq for the following reaction is 0.16:
A (g) + B (g) C (g) + D (g)
The value of Keq at the same temperature for the reaction below is ________.
3C (g) + 3D (g) 3A (g) + 3B (g)
A) 2.4 × 102
B) 2.1
C) 4.1 × 10–3
D) 5.3 × 10-2
E) 6.3
12) The value of Keq for the following reaction is 0.50:
A (g) + 2B (g) C (g) + 4D (g)
The value of Keq at the same temperature for the reaction below is ________.
2
1
A (g) + B (g)
2
1
C (g) + 2D (g)
A) 7.1 × 10-1
B) 2.5 × 10-1
C) 0.25
D) 1.0
E) 0.50
13) The Keq for the equilibrium below is 7.16 × 10-2 at 440.0 °C.
2Cl2 (g) + 2H2O (g) 4HCl (g) + O2 (g)
What is the value of Keq at this temperature for the following reaction?
Cl2 (g) + H2O (g) 2HCl (g) + O2 (g)
A) 0.0716
B) 5.13 × 10-3
C) 0.268
D) 0.0376
E) 0.150
14) At 1000.0 K, the equilibrium constant for the reaction
2NO (g) + Br2 (g) 2NOBr (g)
is Kp = 0.016. Calculate Kp for the reverse reaction,
2NOBr (g) 2NO (g) + Br2 (g).
A) 0.016
B) 1.6 × 10-4
C) 63
D) 0.99
E) 1.1
15) The expression of Keq for the following reaction will not include ________.
A(g) + B (g) C (l) + D (g)
A) [C]
B) [A]
C) [B]
D) [D]
E) none of the above
16) Phosphorous trichloride and phosphorous pentachloride equilibrate in the presence of molecular
chlorine according to the reaction:
PCl3 (g) + Cl2 (g) → PCl5 (g)
An equilibrium mixture at 450 K contains
PPCl3 = 0.224 atm,
PCl2 = 0.284 atm, and
PPCl5 = 4.24 atm. What is the value of Kp at this temperature?
A) 66.7
B) 1.50 × 10-2
C) 2.70 × 10-1
D) 3.74
E) 8.36
17) Consider the following chemical reaction:
H2 (g) + I2 (g) 2HI (g)
At equilibrium in a particular experiment, the concentrations of H2, I2, and HI were 0.20 M, 0.034 M, and
0.55 M, respectively. The value of Keq for this reaction is ________.
A) 23
B) 81
C) 0.0090
D) 5.1
E) 44
18) Dinitrogen tetroxide partially decomposes according to the following equilibrium:
N2O4 (g) → 2NO2 (g)
A 1.000-L flask is charged with 9.20 × 10-3 mol of N2O4. At equilibrium, 5.98 × 10-3 mol of N2O4
remains. Keq for this reaction is ________.
A) 0.183
B) 0.197
C) 0.212
D) 6.94 × 10-3
E) 2.96 × 10-5
19) The Kp for the reaction below is 1.49 × 108 at 100.0 °C:
CO (g) + Cl2 (g) → COCl2 (g)
In an equilibrium mixture of the three gases, PCO = PCl2 = 1.00 × 10–4 atm. The partial pressure of the
product, phosgene (COCl2), is ________ atm.
A) 1.49
B) 1.49 × 1016
C) 6.71 × 10–17
D) 1.49 × 104
E) 1.49 × 1012
20) At 900.0 K, the equilibrium constant (Kp) for the following reaction is 0.345.
2SO2 + O2 (g) → 2SO3 (g)
At equilibrium, the partial pressure of SO2 is 36.9 atm and that of O2 is 16.8 atm. The partial pressure of
SO3 is ________ atm.
A) 88.8
B) 3.89 × 10-3
C) 214
D) 5.57 × 10-4
E) 42.4
21) At elevated temperatures, molecular hydrogen and molecular bromine react to partially form
hydrogen bromide:
H2 (g) + Br2 (g) 2HBr (g)
A mixture of 0.682 mol of H2 and 0.440 mol of Br2 is combined in a reaction vessel with a volume of
2.00 L. At equilibrium at 700 K, there are 0.546 mol of H2 present. At equilibrium, there are ________ mol
of Br2 present in the reaction vessel.
A) 0.000
B) 0.440
C) 0.546
D) 0.136
E) 0.304
22) At 24° C, Kp = 0.080 for the equilibrium:
NH4HS (s) NH3 (g) + H2S (g)
A sample of solid NH4HS is placed in a closed vessel and allowed to equilibrate. Calculate the
equilibrium partial pressure (atm) of ammonia, assuming that some solid NH4HS remains.
A) 0.28
B) 0.080
C) 0.052
D) 0.0049
E) 3.8
23) In the coal-gasification process, carbon monoxide is converted to carbon dioxide via the following
reaction:
CO (g) + H2O (g) CO2 (g) + H2 (g)
In an experiment, 0.35 mol of CO and 0.40 mol of H2O were placed in a 1.00-L reaction vessel. At
equilibrium, there were 0.22 mol of CO remaining. Keq at the temperature of the experiment is ________.
A) 5.5
B) 0.75
C) 3.5
D) 0.28
E) 1.0
24) Kp = 0.0198 at 721 K for the reaction
2HI (g) H2 (g) + I2 (g)
In a particular experiment, the partial pressures of H2 and I2 at equilibrium are 0.678 and 0.788 atm,
respectively. The partial pressure of HI is ________ atm.
A) 7.87
B) 27.0
C) 5.19
D) 0.103
E) 0.0106
25) Nitrosyl bromide decomposes according to the following equation.
2NOBr (g) 2NO (g) + Br2 (g)
A sample of NOBr (0.64 mol) was placed in a 1.00-L flask containing no NO or Br2. At equilibrium the
flask contained 0.16 mol of NOBr. How many moles of NO and Br2, respectively, are in the flask at
equilibrium?
A) 0.48, 0.24
B) 0.48, 0.48
C) 0.16, 0.08
D) 0.16, 0.16
E) 0.24, 0.42
33
26) The reaction below is exothermic:
2SO2 (g) + O2 (g) 2SO3 (g)
Le Châtelier’s Principle predicts that ________ will result in an increase in the number of moles of SO3 (g)
in the reaction container.
A) increasing the amount of SO2
B) decreasing the pressure
C) increasing the temperature
D) removing some oxygen
E) increasing the volume of the container
27) For the endothermic reaction
CaCO3 (s) CaO (s) + CO2 (g)
Le Châtelier’s principle predicts that ________ will result in an increase in the number of moles of CO2.
A) increasing the temperature
B) decreasing the temperature
C) increasing the pressure
D) removing some of the CaCO3(s)
E) none of the above
28) Consider the following reaction at equilibrium:
2NH3 (g) N2 (g) + 3H2 (g) ΔH° = +92.4 kJ
Le Châtelier’s principle predicts that removing N2 (g) to the system at equilibrium will result in ________.
A) an increase in the concentration of H2
B) a decrease in the concentration of H2
C) removal of all of the H2
D) a lower partial pressure of H2
E) an increase in the value of the equilibrium constant
29) Consider the following reaction at equilibrium:
2CO2 (g) 2CO (g) + O2 (g) ΔH° = -514 kJ
Le Châtelier’s principle predicts that removing O2 (g) to the reaction container will ________.
A) increase the partial pressure of CO
B) decrease the partial pressure of CO
C) increase the partial pressure of CO2
D) increase the value of the equilibrium constant
E) decrease the value of the equilibrium constant
30) Consider the following reaction at equilibrium:
C (s) + H2O (g) CO (g) + H2 (g)
Which of the following conditions will decrease the partial pressure of CO?
A) decreasing the volume of the reaction vessel
B) increasing the volume of the reaction vessel
C) decreasing the amount of carbon in the system
D) decreasing the pressure of the reaction vessel
E) adding a catalyst to the reaction system
31) Consider the following reaction at equilibrium:
2SO2 (g) + O2 (g) 2SO3 (g) ΔH° = -99 kJ
Le Châtelier’s principle predicts that a(n) increase in temperature will result in ________.
A) an increase in the partial pressure of O2
B) a decrease in the partial pressure of O2
C) a decrease in the partial pressure of SO2
D) a(n) increase in Keq
E) no changes in equilibrium partial pressures
35
15.4 Short Answer Questions
1) The equilibrium-constant expression for a reaction written in one direction is the ________ of the one
for the reaction written for the reverse direction.
2) If Reaction A + Reaction B = Reaction C, then Kc Reaction C = ________.
3) If the value for the equilibrium constant is much greater than 1, then the equilibrium mixture contains
mostly ________.
4) Pure ________ and pure ________ are excluded from equilibrium-constant expressions.
5) Exactly 3.5 moles if N2O4 is placed in an empty 2.0-L container and allowed to reach equilibrium
described by the equation
N2O4 (g) ⇌ 2NO2 (g)
If at equilibrium the N2O4 is 25% dissociated, what is the value of the equilibrium constant for the
reaction?
6) The number obtained by substituting starting reactant and product concentrations into an equilibrium–
constant expression is known as the ________.
7) If the reaction quotient Q for a reaction is less than the value of the equilibrium constant K for that
reaction at a given temperature, ________ must be converted to ________ for the system to reach
equilibrium.
8) If the reaction quotient Q for a reaction is greater than the value of the equilibrium constant K for that
reaction at a given temperature, ________ must be converted to ________ for the system to reach
equilibrium.
9) For an exothermic reaction, increasing the reaction temperature results in a(n) ________ in K.
10) If a reaction is endothermic, ________ the reaction temperature results in an increase in K.
15.5 True/False Questions
1) The relationship between the concentrations of reactants and products of a system at equilibrium is
given by the law of mass action.
2) The effect of a catalyst on a chemical reaction is to react with product, effectively removing it and
shifting the equilibrium to the right.
3) At constant temperature, reducing the volume of a gaseous equilibrium mixture causes the reaction to
shift in the direction that increases the number of moles of gas in the system.
4) In an exothermic equilibrium reaction, increasing the reaction temperature favors the formation of
reactants.
5) Le Châtelier’s principle states that if a system at equilibrium is disturbed, the equilibrium will shift to
minimize the disturbance.