46) Consider the following reaction at equilibrium.
2CO2 (g) 2CO (g) + O2 (g) ΔH° = -514 kJ
Le Châtelier’s principle predicts that the equilibrium partial pressure of CO (g) can be maximized by
carrying out the reaction __________.
A) at high temperature and high pressure
B) at high temperature and low pressure
C) at low temperature and low pressure
D) at low temperature and high pressure
E) in the presence of solid carbon
47) Consider the following reaction at equilibrium:
2SO2 (g) + O2 (g) 2SO3 (g) ΔH° = -99 kJ
Le Châtelier’s principle predicts that an increase in temperature will result in __________.
A) a decrease in the partial pressure of SO3
B) a decrease in the partial pressure of SO2
C) an increase in Keq
D) no changes in equilibrium partial pressures
E) the partial pressure of O2 will decrease
48) The effect of a catalyst on an equilibrium is to __________.
A) increase the rate of the forward reaction only
B) increase the equilibrium constant so that products are favored
C) slow the reverse reaction only
D) increase the rate at which equilibrium is achieved without changing the composition of the
equilibrium mixture
E) shift the equilibrium to the right
15.2 Bimodal Questions
1) The value of Keq for the equilibrium
H2 (g) + I2 (g) 2 HI (g)
is 794 at 25 °C. What is the value of Keq for the equilibrium below?
1/2 H2 (g) + 1/2 I2 (g) HI (g)
A) 397
B) 0.035
C) 28
D) 1588
E) 0.0013
2) The value of Keq for the equilibrium
H2 (g) + I2 (g) 2 HI (g)
is 794 at 25°C. At this temperature, what is the value of Keq for the equilibrium below?
HI (g) 1/2 H2 (g) + 1/2 I2 (g)
A) 1588
B) 28
C) 397
D) 0.035
E) 0.0013
3) The value of Keq for the equilibrium
H2 (g) + I2 (g) 2 HI (g)
is 54.0 at 427°C. What is the value of Keq for the equilibrium below?
HI (g) 1/2 H2 (g) + 1/2 I2 (g)
A) 27
B) 7.35
C) 0.136
D) 2.92 × 103
E) 3.43 × 10-4
4) The value of Keq for the equilibrium
CO2 (g) + 2H2 (g) CH3OH (g)
is 14.5 at 483 °C. What is the value of Keq for the equilibrium below?
1/2 CO2 + H2 (g) 1/2 CH3OH (g)
A) 7.30
B) 7.35
C) 0.136
D) 3.81
E) 6.90 × 10-2
5) The value of Keq for the equilibrium
N2 (g) + O2 (g) 2 NO (g)
is 4.2 × 10-31 at 27 °C. What is the value of Keq for the equilibrium below?
4 NO (g) 2 N2 (g) + 2 O2 (g)
A) 5.7 × 1060
B) 8.4 × 10-31
C) 4.2 × 1031
D) 8.4 × 1031
E) none of the above
6) Consider the following chemical reaction:
CO (g) + 2H2 (g) CH3OH(g)
At equilibrium in a particular experiment, the concentrations of CO and H2 were 0.15 M and0.36
M,respectively. What is the equilibrium concentration of CH3OH? The value of Keq for this reaction is
14.5 at the temperature of the experiment.
A) 14.5
B) 7.61 × 10-3
C) 2.82 × 10-1
D) 3.72 × 10-3
E) 1.34 × 10-3
7) A reaction vessel is charged with hydrogen iodide, which partially decomposes to molecular
hydrogen and iodine:
2HI (g) H2(g) + I2(g)
When the system comes to equilibrium at 425 °C, PHI = 0.708 atm, and PH2 = PI2 = 0.0960 atm. The
value of Kp at this temperature is __________.
A) 6.80 × 10-2
B) 1.30 × 10-2
C) 54.3
D) 1.84 × 10-2
E) Kp cannot be calculated for this gas reaction when the volume of the reaction vessel is not given.
8) Acetic acid is a weak acid that dissociates into the acetate ion and a proton in aqueous solution:
HC2H3O2 (aq) C2H3O2– (aq) + H+ (aq)
At equilibrium at 25 °C a 0.100 M solution of acetic acid has the following concentrations: [HC2H3O2]
= 0.0990 M, [C2H3O2–] = 1.33 × 10-3 M, and [H+] = 1.33 × 10-3 M. The equilibrium constant, Keq,
for the ionization of acetic acid at 25°C is __________.
A) 5.71 × 104
B) 0.100
C) 1.75 × 10-7
D) 1.79 × 10-5
E) 5.71 × 106
9) Dinitrogentetraoxide partially decomposes according to the following equilibrium:
N2O4 (g) 2NO2 (g)
A 1.00-L flask is charged with 0.0400 mol of N2O4. At equilibrium at 373 K, 0.0055 mol of N2O4
remains. Keq for this reaction is __________.
A) 2.2 × 10-4
B) 13
C) 0.22
D) 0.022
E) 0.87
10) Given the following reaction:
CO (g) + 2H2(g) CH3OH (g)
In an experiment, 0.42 mol of CO and 0.42 mol of H2 were placed in a 1.00-L reaction vessel. At
equilibrium, there were 0.29 mol of CO remaining. Keq at the temperature of the experiment is
__________.
A) 2.80
B) 0.357
C) 14.5
D) 17.5
E) none of the above
11) A sealed 1.0 L flask is charged with 0.500 mol of I2 and 0.500 mol of Br2. An equilibrium reaction
ensues:
I2 (g) + Br2 (g) 2IBr (g)
When the container contents achieve equilibrium, the flask contains 0.84 mol of IBr. The value of Keq is
__________.
A) 11
B) 4.0
C) 110
D) 6.1
E) 2.8
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) Given the following reaction at equilibrium, if Kc = 6.34 x 105 at 230.0°C, Kp = __________.
2NO (g) + O2 (g) 2NO2 (g)
A) 3.67 × 10-2
B) 1.53 × 104
C) 6.44 × 105
D) 2.61 × 106
E) 2.62 × 107
2) Given the following reaction at equilibrium at 450.0°C:
CaCO3 (s) CaO (s) + CO2 (g)
If pCO2 = 0.0135 atm, Kc = __________.
A) 135
B) 0.0821
C) 0.801
D) 2.27 × 10-4
E) 8.01
3) Given the following reaction at equilibrium, if Kp = 0.990 at 250.0°C, Kc = __________.
PCl5 (g) PCl3 (g) + Cl2 (g)
A) 3.90 × 10-6
B) 2.31 × 10-2
C) 0.990
D) 42.9
E) 42.5
4) Given the following reaction at equilibrium at 300.0 K:
NH4HS (s) NH3 (g) + H2S (g)
If pNH3 = pH2S = 0.109 atm, Kp = __________.
A) .0119
B) 4.99 × 10-4
C) .109
D) .0821
E) 5.66 × 10-3
5) The Keq for the equilibrium below is 7.73 × 10-2 at 500.0°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) +
1
2
O2 (g)
A) 0.0773
B) 5.98 × 10-3
C) 0.278
D) 0.0376
E) 0.150
6) At 1000.0 K, the equilibrium constant for the reaction
2NO (g) + Br2 (g) 2NOBr (g)
is Kp = 0.017. Calculate Kp for the reverse reaction,
2NOBr (g) 2NO (g) + Br2 (g).
A) 0.017
B) 1.6 × 10-4
C) 59
D) 0.99
E) 1.1
7) 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 = 0.124 atm,
PCl2 = 0.157 atm, and
PPCl5 = 1.30 atm. What is the value of Kp at this temperature?
A) 66.7
B) 1.50 × 10-2
C) 2.53 × 10-2
D) 1.02
E) 4.63
8) 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 0.25 M, 0.035 M,
and 0.55 M, respectively. The value of Keq for this reaction is __________.
A) 23
B) 63
C) 0.0090
D) 5.1
E) 34
9) Dinitrogen tetroxide partially decomposes according to the following equilibrium:
N2O4 (g) 2NO2 (g)
A 1.000-L flask is charged with 3.00 × 10-2 mol of N2O4. At equilibrium, 2.36 × 10-2 mol of N2O4
remains. Keq for this reaction is __________.
A) 0.723
B) 0.391
C) 0.212
D) 6.94 × 10-3
E) 1.92 × 10-4
10) 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 = 2.22 × 10-4 atm. The partial pressure of
the product, phosgene (COCl2), is __________ atm.
A) 7.34
B) 3.02 × 1015
C) 3.31 × 10-16
D) 3.31 × 104
E) 6.67 × 1011
11) 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 35.0 atm and that of O2 is 15.9 atm. The partial pressure of
SO3 is __________ atm.
A) 82.0
B) 4.21 × 10-3
C) 192
D) 6.20 × 10-4
E) 40.2
12) 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 0.556 mol of H2 present. At equilibrium, there are
__________ mol of Br2 present in the reaction vessel.
A) 0.000
B) 0.440
C) 0.556
D) 0.126
E) 0.314
13) At 27°C, Kp = 0.095 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) 0.31
B) 0.095
C) 0.052
D) 0.0049
E) 3.8
14) 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 0.16 mol of CO remaining. Keq at the temperature of the experiment is
__________.
A) 5.5
B) 0.75
C) 0.93
D) 1.1
E) 1.0
15) 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 0.836 and 0.701 atm,
respectively. The partial pressure of HI is __________ atm.
A) 7.87
B) 29.6
C) 5.44
D) 0.108
E) 0.0116
16) 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 0.36 mol of NOBr. How many moles of NO and Br2, respectively, are in the flask at
equilibrium?
A) .28,.28
B) .36,.18
C) .28,.14
D) .14,.23
E) .36,.36
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(an) __________ 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.