Princeton 2012/Barron 4th ed.
AP Practice Problems
Unit 12 – Equilibrium
Multiple Choice (no calculator)
For questions 1-3, one or more of the
following responses will apply; each
response may be used more than once or not
at all in these questions.
A.
B.
C.
D.
E.
Kc
Kp
Ka
Kw
Ksp
1. This equilibrium constant uses
partial pressures of gases as units.
(P10.1)
2. This equilibrium constant is used for
the dissociation of an acid. (P10.2)
3. The equilibrium expression for this
equilibrium constant does not
contain a denominator. (P10.4)
4. A gaseous reaction occurs and comes
to equilibrium as shown below.
Which of the following changes to
the system will serve to increase the
number of moles of I2 present at
equilibrium? (P10.6)
2HI(g) + Cl2(g) ↔ 2HCl(g) + I2(g) + energy
a. Increasing the volume at a
constant temperature
b. Decreasing the volume at a
constant temperature
c. Adding a mole of inert gas at
constant volume
d. Increasing the temperature at
constant volume
e. Decreasing the temperature at
constant volume.
5. A sealed isothermal container
initially contained 2 moles of CO gas
and 3 moles of H2 gas. The
following reversible reaction
occurred:
CO(g) + 2H2(g) ↔ CH3OH(g)
At equilibrium, there was 1 mole of
CH3OH in the container. What was
the total number of moles of gas
present in the container at
equilibrium? (P10.7)
a.
b.
c.
d.
e.
1
2
3
4
5
6. Which of the following changes to
the system at equilibrium shown
below would cause the concentration
of H2O to increase? (P10.8)
4NH3(g) + 3O2(g) ↔ 2N2(g) + 6H2O(g) +
energy
a. The volume of the system
was decreased at constant
temperature.
b. The temperature of the
system was increased at
constant volume.
c. NH3 was removed from the
system.
d. N2 was removed from the
system.
e. O2 was removed from the
system.
Princeton 2012/Barron 4th ed.
7. A sample of solid potassium nitrate
is placed in water. The solid
potassium nitrate comes to
equilibrium with its dissolved ions
by the endothermic process shown
below.
KNO3(s) + energy ↔ K+(aq) + NO3-(aq)
Which of the following changes to
the system would increase the
concentration of K+ ions at
equilibrium? (P10.9)
a. The volume of the solution is
increased.
b. The volume of the solution is
decreased.
c. Additional solid KNO3 is
added to the solution.
d. The temperature of the
solution is increased.
e. The temperature of the
solution is decreased.
8. For which of the following gaseous
equilibria to Kp and Kc differ the
most? (P10.10)
a. 2H2(g) + O2(g) ↔ 2H2O(g)
b. NH3BH3(g) ↔ NH2BH2(g) +
H2(g)
c. NO(g) + O3(g) ↔ NO2(g) +
O2(g)
d. B3N3H3(g) + 3H2(g) ↔
B3N3H12(g)
e. BH3(g) + 3HCl(g) ↔ BCl3(g)
+ 3H2(g)
9. The reaction below came to
equilibrium at a temperature of
100°C. At equilibrium the partial
pressure due to NOBr was 4
atmospheres, the partial pressure due
to NO was 4 atmospheres, and the
partial pressure due to Br2 was 2
atmospheres. What is the
equilibrium constant, Kp, for the
reaction at 100°C? (P10.12)
2NOBr(g) ↔ 2NO(g) + Br2(g)
a.
b.
c.
d.
e.
¼
½
1
2
4
10. At 150°C, the equilibrium constant,
Kc, for the reaction shown below has
a value of 300. This reaction was
allowed to reach equilibrium in a
sealed container and the partial
pressure due to IBr(g) was found to
be 3 atm. Which of the following
could be the partial pressures due to
Br2(g) and I2(g) in the container?
(P10.14)
Br2(g) + I2(g) ↔ 2IBr(g)
a.
b.
c.
d.
e.
Br2(g)
0.1 atm
0.3 atm
1 atm
1 atm
3 atm
I2(g)
0.3 atm
1 atm
1 atm
3 atm
3 atm
Princeton 2012/Barron 4th ed.
11. Initially, a sealed vessel contained
only H2(g) with a partial pressure of
6 atm and CO2(g) with a partial
pressure of 4 atm. The reaction
below was allowed to come to
equilibrium at a temperature of
700K. At equilibrium, the partial
pressure due to CO(g) was found to
be 2 atm. What is the value of the
equilibrium constant Kp, for the
reaction? (P10.15)
H2(g) + CO2(g) ↔ H2O(g) + CO(g)
a.
b.
c.
d.
e.
1/24
1/6
1/4
1/3
1/2
For questions 12-14, one or more of the
following responses will apply; each
response may be used more than once or not
at all in these questions.
I.
II.
III.
IV.
V.
Ka
Ksp
Q
Kc
Le Chatlier’s Principle
12. The effect of temperature on a
chemical system is best described
using (B10.1)
a.
b.
c.
d.
e.
I and III
II
III and V
IV
V
13. This is the correct term to use to
determine if a system has come to
equilibrium (B10.2)
a.
b.
c.
d.
e.
I and III
II
III
IV
V
14. The term(s) most useful in
determining the solubility of a
substance is (are) (B10.3)
a.
b.
c.
d.
e.
I and III
II
III and V
IV
V
15. A chemical system in equilibrium
will (B10.4)
a. have the same concentrations
of all products and reactants
b. form more products if the
temperature is increased
c. have a specific ratio of
products to reactants
d. not have any precipitates
e. represent a spontaneous
chemical process
16. Which of the following CANNOT
affect the extent of reaction?
(B10.16)
a. Changing the temperature
b. Adding a catalyst
c. Increasing the amounts of
reactants
d. Removing some product
e. Changing the volume
Princeton 2012/Barron 4th ed.
17. In which of the following cases is the
reaction expected to be exothermic?
(B10.17)
a. Increasing the pressure
increases the amount of
product formed.
b. Increasing the amount of
reactants increases the
amount of product formed.
c. Increasing the temperature
increases the amount of
product formed.
d. Increasing the volume
decreases the amount of
product formed.
e. Increasing the temperature
decreases the amount of
product formed.
Princeton 2012/Barron 4th ed.
Essays
1. When the reaction below took place at a temperature of 570 K, the following equilibrium
concentrations were measured (P10.3):
N2(g) + 3H2(g) ↔ 2NH3(g)
∆H = -92.4 kJ
[NH3] = 0.20 mol/L
[N2] = 0.50 mol/L
[H2] = 0.20 mol/L
a. Write the expression for Kc and calculate its value.
b. What is the value of Kp for the reaction?
c. Describe how the concentration of H2 will be affected by each of the following
changes to the system at equilibrium:
i.
The temperature is increased.
ii.
The volume of the reaction chamber is increased.
iii.
N2 gas is added to the reaction chamber.
iv.
Helium gas is added to the reaction chamber.
2. At a certain temperature, the reaction of hydrogen and chlorine to produce hydrogen
chloride, all in the gas phase, has an equilibrium constant of 265. If 25.0 g of HCl is
placed in a 150-L vessel and allowed to come to equilibrium, what will the
concentrations of all species be? (B10.1)
Princeton 2012/Barron 4th ed.
Answers – Equilibrium
Multiple Choice
1. B
2. C
3. E
4. E
5. C
6. D
7. D
8. D
9. D
10. A
11. E
12. E
13. C
14. B
15. C
16. B
17. E
Essays
1. a. Kc = 10
b. Kp = 4.7×10-3
c. (i) increase (ii) increase (iii) decrease (iv) no effect
2. [H2] = 2.50×10-4; [Cl2] = 2.50×10-4; [HCl] = 4.07×10-3