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1.
Practice Questions
Equilibrium
7. HC 2H3O2(aq) + H2O(l) ® H3O+ (aq) + C 2H3O2– (aq)
CaCO3(s) « Ca2+(aq) + CO32–(aq)
Which of the following reagents, when added to the
above equilibrium system, would cause more CaCO3 to
dissolve?
1) KNO3(s)
3) Na2C2O3(s)
5) H2C2O4(s)
What is the correct equilibrium expression for the
above reaction?
1)
2) CaCO3(s)
2)
4) HBrO 4(s)
3)
2. Which of the following apply to all equilibrium systems?
I. Forward and reverse rates are equal
II. Macroscopic properties are constant
III. Mass of reactants equals mass of products
1) I only
3) I and III only
5) I, II and III
2) I and II only
4) II and III only
4)
2) NaNO3
4) Mg(NO3) 2
4. If Q is the reaction quotient and K is the equilibrium
constant for a chemical reaction, which of the following
will result in the reaction proceeding towards the right
(producing more products)?
1) Q < K
3) Q > K
5) None of the above
9.
2) Q = K
4) Q is constant
10.
3)
4)
N2(g) + 3 H2(g) «2 NH3 (g)
0.4 mole of ammonia results after 1.2 mole of nitrogen
gas is combined with 1.8 mole of hydrogen gas in a 1.0
L flask. What is the K eq for this reaction?
1) 0.45
2) 0.34
3) 0.29
4) 0.12
5) 0.02
2)
3)
4)
2H2O(g) « 2H2(g) + O2(g)
When 0.1010 mol H2O is placed in a 1.000 L container,
equilibrium is established. The equilibrium
concentration of O2 is 0.0010 M. What are the
equilibrium concentrations of H2O and H 2?
1)
2)
3)
4)
5)
1)
2)
1)
5)
5. 20 HNO3(aq) + 3 P 4(s) + 8 H2O(l) + Heat « 12 H3PO 4(aq) + 20 NO(g)
What is the equilibrium law expression for the above
reaction?
6.
5)
8. Which equation is the correct equilibrium expression for
the hydrolysis of SO 42–?
3. Magnesium carbonate would be most soluble in a
solution of
1) MgCl 2
3) Na2CO 3
5) Na3PO 4
Date____________
[H2O] = 0.1015; [H 2] = 0.0040
[H2O] = 0.1000; [H 2] = 0.0010
[H2O] = 0.1005; [H 2] = 0.0005
[H2O] = 0.1010; [H 2] = 0.0020
[H2O] = 0.0990; [H2] = 0.0020
H2O(g) + CO(g) « H2(g) + CO2(g)
A closed container is initially filled with H 2O and CO.
As the reaction proceeds towards equilibrium the
1)
2)
3)
4)
5)
[CO] and [CO2] both increase
[CO] and [CO 2] both decrease
[CO] increases and [CO 2] decreases
[CO] decreases and [CO2] increases
[CO] decreases and [CO2] remains constant
Practice Questions
11.
N2O4(g) « 2NO2(g)
A 1.00 L container is initially filled with 0.200 mol N2
O4. N2O4 breaks down as shown in the above
equilibrium reaction. At equilibrium, 0.160 mol NO2
are present. What is the equilibrium concentration of
N 2O 4?
1) 0.040 mol/L
3) 0.120 mol/L
5) 0.190 mol/L
12.
13.
[H3O+] has increased and the [OH –] has increased
[H3O+] has decreased and the [OH–] has decreased
[H3O+] has decreased and the [OH–] has increased
[H3O+] has decreased and the [OH–] has remained
the same
[H3O+] and pH both decreased
[H3O+] and pH both increased
[H3O +] increased and pH decreased
[H3O+] decreased and pH increased
[H3O+] and pH remained the same
I2(s) + H2O(l) « H+(aq) + I–(aq) + HIO(aq)
What is the equilibrium constant for the reaction
above?
1)
2)
3)
4)
5)
17.
N2(g) + 3 H2(g) « 2 NH3(g) + 22 kcal
According to the above reaction, which additions or
removals will increase the yield (the amount produced)
of NH 3(g)?
1)
2)
3)
4)
5)
Add N 2, H2, NH 3, and pressure; remove heat.
Add N 2, H2, and heat; remove NH 3 and pressure.
Add NH3 and heat; remove N2, H2, and pressure.
Add N 2, H2, and NH 3; remove pressure and heat.
Add N2, H2, and pressure; remove NH3 and heat.
Base your answers to questions 18 through 23 on the
equation and the choices provided.
CN –(aq) + H2O(l) « HCN(aq) + OH –(aq)
(A) increases
(B) decreases
(C) remains the same
(D) increases, then decreases
(E) decreases, then increases
18. If CN– is removed, the Keq
2 H2O(l) ® H3O+(aq) + OH–(aq)
1) A
2) B
3) C
After the above reaction reaches equilibrium, a small
19. If CN– is added, the [CN–]
3+
amount of Fe(H 2O)6 is added to water and equilibrium
1) A
2) B
3) C
is re-established. Which of the following represent the
changes in the net ion concentrations?
20. If OH– is added, the [H 2O]
4) D
5) E
4) D
5) E
4) D
5) E
4) D
5) E
1) A
2) B
3) C
4) D
PCl5(g) « PCl3(g) + Cl2(g)
At equilibrium, [PCl 5] is 0.400 M, [PCl 3] is 1.50 M and 23. If the pressure is increased, the [OH –]
[Cl2] is 0.600 M. The K eq for the reaction above is
1) A
2) B
3) C
4) D
1) 0.360 2) 0.444 3) 0.900 4) 2.25
5) 2.50
5) E
1)
2)
3)
4)
5)
15.
[H3O +] has increased and the [OH–] has decreased
2 H2O(l) « H3O+(aq) + OH–(aq)
A small amount of HCl is added to water and
equilibrium is reestablished. When comparing the new
equilibrium with the original equilibrium, which of the
following observations can be made?
1)
2)
3)
4)
5)
14.
2) 0.080 mol/L
4) 0.160 mol/L
2 H2O(l) « H3O+(aq) + OH–(aq)
A few drops of 1.0 M HCl are added to the above
system. When equilibrium is reestablished, the
1)
2)
3)
4)
5)
16.
[H3O+] increases; [OH–] increases
+
–
[H O ] increases; [OH ] decreases
3
[H3O+] decreases; [OH –] decreases
[H3O+] decreases; [OH –] increases
[H3O+] no change; [OH –] increases
1) A
2) B
3) C
21. If HCN is removed, the [HCN]
1) A
2) B
3) C
22. If H 2O is removed, the [CN –]
5) E
Practice Questions
Base your answers to questions 24 through 27 on the
equation and the choices provided.
31.
CaCO3(s) + Heat « CaO(s) + CO2(g)
(A) increases
(B) decreases
(C) remains the same
(D) increases, then decreases
(E) decreases, then increases
24. If the pressure is decreased, the [CO 2]
1) A
2) B
3) C
4) D
1)
2)
3)
4)
2) B
3) C
4) D
5) E
5) E
26. If temperature is decreased, the [CO2]
1) A
2) B
3) C
4) D
5) E
27. If the pressure is increased, the K
1) A
2) B
3) C
4) D
5) E
28. For which of the following reactions will an increase in
pressure result in an increase in product?
1)
2)
3)
4)
5)
N2(g) +3 H2(g) « 2 NH3(g)
CO 2(g) + SO2(g) « SO 3(g) + CO(g)
MgCO 3(aq) « MgO(s) + O2(g)
H2(g) + F 2(g) « 2 HF(g)
2 HgO(s) « O2(g) + 2 Hg(l)
29. In which of the following reactions will an increase in
pressure result in a shift to the RIGHT at equilibrium?
1)
2)
3)
4)
5)
2 NH 3(g) « 3 H2(g) + N2(g)
H2(g) + Cl 2(g) « 2 HCl(g)
Cl 2(g) « 2 Cl(g)
2 H 2(g) + O2(g) « 2 H2O(g)
Cl 2O(g) « ½ O2(g) + Cl 2(g)
30. Base your answer to the following question on the
reaction below, where equilibrium has been established
N2 (g) + 3 H2 (g) « 2 NH3 (g) + heat
If N 2 is added to this closed system, which of the
following will have a lower value than at the original
equilibrium?
1)
2)
3)
4)
5)
The amount of nitrogen gas in the system
The amount of hydrogen gas in the system
The amount of ammonia gas in the system
The total pressure of the closed system
The temperature of the closed system
Forward rate: decreased; reverse rate: decreased
Forward rate: increased; reverse rate: increased
Forward rate: decreased; reverse rate: increased
Forward rate: remained constant; reverse rate:
remained constant
5) Forward rate: increased; reverse rate: decreased
25. If the temperature is decreased, the K eq
1) A
H2(g) + I2(g) ® 2 HI(g)
The volume of the equilibrium reaction is increased and
a new equilibrium is established. Compared to the
rates in the original equilibrium, which of the following
describes the rates of the forward and reverse reactions
in the new equilibrium?
32.
COCl2(g) « CO(g) + Cl2(g)
When the reaction above is at equilibrium in a 1.0 L
container, there are 3.0 mol COCl 2, 0.49 mol CO and
0.49 mol Cl 2. At constant temperature the volume of
the system above is decreased to 0.50 L. Which of the
following occurs when equilibrium is restored?
1) [COCl2] has increased while [CO] and [Cl 2]
decreased
2) [COCl2] has decreased while [CO] and [Cl 2]
increased
3) Concentrations of all three gases have decreased
4) Concentrations of all three gases have increased
5) [COCl2] and [CO] increased and [Cl 2] decreased
33. Base your to the following question on the reaction
below.
A: 2 S(g) + 3 O2(g) « 2 SO3(g)
After equilibrium in reaction A has been established,
pure S(g) is injected into the reaction container at
constant temperature. What is true of the system after
equilibrium has been reestablished?
1) The total pressure of the system is changed
2) The K eq is changed
3) The amount of S(g) in the reaction container has
decreased from its original value in the first
equilibrium
4) The amount of SO3(g) in the reaction container has
decreased from its original value in the first
equilibrium
5) The amount of O2(g) in the reaction container has
decreased from its original value in the first
equilibrium
Practice Questions
34.
Fe3+(aq) + SCN–(aq) « FeSCN2+(aq)
What happens to the concentrations of the three ions
when some Fe 3+ ion is removed by precipitation from
the above aqueous solution, with the temperature
remaining constant?
37.
Fe3+(aq) + SCN–(aq) « FeSCN2+(aq)
What happens to the concentrations of the three ions
when some KSCN(s) (a source of SCN– ion) is added
to the above aqueous solution.
1)
1)
2)
2)
3)
3)
4)
4)
38.
Base your answers to questions 35 and 36 on the
equation and the choices provided.
2 SO 2(g) + O2(g) « 2 SO 3(g) + 46.8 kcal
(A) increases
(B) decreases
(C) remains the same
(D) increases, then decreases
(E) decreases, then increases
35. If temperature is decreased, the Keq
1) A
2) B
3) C
4) D
5) E
4) D
5) E
36. If a catalyst is added, the [SO3]
1) A
2) B
3) C
N2(g) + 3 H2(g) « 2 NH3 + 22 kcal
Which shows what happens to the concentrations of the
three gases when some H 2 is added to the above
equilibrium system with temperature and pressure
remaining constant?
1)
2)
3)
4)
Practice Questions
39.
PCl3(g) + Cl2(g) « PCl5(g)
What will be the effect of doubling the PCl 3(g)
concentration?
1)
2)
3)
4)
5)
40.
[Cl 2(g)] will decrease
I. Increase in pressure. II. Increase in temperature.
III. Introduction of a catalyst.
1) I only
3) III only
5) I, II, and III
42.
2) II only
4) I and II only
4 HBr(g) + O2(g) « 2 H2O(g) + 2 Br2(g)
DH = – 276kJ
Which change to the above system at equilibrium will
increase the concentration of Br 2(g)?
1)
2)
3)
4)
5)
44.
left and [SO2Cl2] increases
left and [SO 2Cl 2] decreases
right and [SO 2Cl 2] decreases
right and [SO 2Cl 2] decreases
right and [SO 2Cl 2] remains constant
45. 2 H2O(l) + 57 kJ « H3O+(aq) + OH –(aq)
When the temperature is decreased in the above
equilibrium, the water
1)
2)
3)
4)
5)
stays neutral and [H 3O+] increases
stays neutral and [H 3O +] decreases
becomes basic and [H3O+] increases
becomes basic and [H3O+] decreases
becomes basic and [OH –] decreases
46. H2(g) + CO2(g) « CO(g) + H2O(g) DH=+41 kJ
The temperature of the above system at equilibrium is
increased while kept at a constant volume. Which of
the following will be true in the new equilibrium
system?
1)
2)
3)
4)
5)
An increase in pressure
An increase in temperature
The removal of oxygen, O 2
The addition of water vapor, H 2O(g)
The removal of HBr(g)
A decrease in the temperature of the reaction
chamber
SO2Cl2(g) + energy « SO2(g) + Cl2(g)
When the temperature is decreased, the above
equilibrium shifts
1)
2)
3)
4)
5)
[NO(g)] will increase more than[O 2(g)]
[NO(g)] will decrease at the same rate as [O 2(g)]
[NO(g)] will increase at the same rate as [O 2(g)]
[NO(g)] and [O2(g)] will remain the same
2 SO3(g) « 2 S(s) + 3 O2(g)
Which of the following causes more oxygen to be
produced?
A decrease in the total pressure
A decrease in the concentration of H 2(g)
An increase in the volume of the reaction chamber
5) A decrease in the concentration of N 2(g)
[NO(g)] will decrease more than [O2(g)]
41. The following endothermic reaction occurs in a rigid
container. N2(g) + 3 H2(g) « 2 NH3(g) + 24 kcal
Which change will increase the above equilibrium
concentration of ammonia, NH 3?
1)
2)
3)
4)
[PCl 5(g)] will decrease
Keq will decrease
Keq will increase
Equilibrium will never be established under these
new conditions
2 NO(g) + O2(g) « N2O4(g)
What will be the effect of halving the N 2O4(g)
concentration?
1)
2)
3)
4)
5)
43.
47.
An increase in [CO] and a decrease in K eq
An increase in [CO] and a increase in Keq
An increase in [CO2] and a decrease in K eq
An increase in [CO2] and a increase in Keq
An decrease in [CO 2] and a decrease in K eq
2 HI(g) «H2(g) + I2(g)
If the above reaction (Keq = 0.020) occurs in a 20
L reaction vessel with 40.0 moles of HI, what is the
concentration of H2(g) left after the reaction has
reached equilibrium?
1) 0.04 M
3) 0.20 M
5) 0.32 M
2) 0.08 M
4) 0.28 M
Practice Questions
48.
2 HI(g) « H2(g) + I2(g) DH = –68 kJ
Which of the following would cause the above
equilibrium to shift to the right?
1) Increasing the temperature while decreasing the
volume
2) Decreasing the volume
3) Increasing the volume
4) Increasing the temperature
5) Decreasing the temperature
49.
1) I only
3) I and II, only
5) I , II, and III
2 A(g) + B(g) « C(g) + 2 D(g)
Gases C and D form from A and B according to the
equation above. At equilibrium [A] = 2.0 M, [B] = 3.0
M, [C] = 4.0 M and [D] = 9.0 M. What is the numerical
value of the equilibrium constant, K, at this
temperature?
1) 0.17
53.
2 NO(g) + O2(g) « 2 NO2(g) + energy
2 mol NO is mixed with 1 mol oxygen in a container at
a temperature of 180 K. Which of the following would
decrease the amount of NO present at equilibrium?
I. Raising the temperature.
II. Adding a mole of Kr at constant volume.
III. Moving everything to a smaller container.
50.
52.
2) 6.0
2) III only
4) II and III, only
CS2(g) + 4 H2(g) « CH4(g) + 2 H2S(g)
The original equilibrium concentrations in the system
above are all 0.60 M. Temperature and pressure may not be constant. Which are possible sets of equilibrium
concentrations?
1) I and V only
3) IV, and V only
5) I, III, and V only
51. At equilibrium, represented by the equation below, the
[NO] is 2.0 M; [O2] is 3.0 M; [N2O5] is 8.0 M.
4 NO(g) + 3 O2(g) « 2 N2O5(g) + Heat
What is the numerical value of the equilibrium
constant, K, at this temperature?
1) 0.15
2) 0.94
3) 1.5
4) 1.6
5) 9.4
56.
2) 2.0 moles/liter
4) 4.5 moles/liter
2) 40.8 %
4) 0.408 %
½ N2(g) + O2(g) « NO2(g) K1 2 NO2(g) « N2
O4(g) K2 N2O4(g) « N2(g) + 2 O2(g)
Given that the above two reactions have equilibrium
constants K 1 and K2 respectively, what would be the
expression for the equilibrium constant K for the third
equation, in terms of K1 and K2 ?
1) K1 K2
3) K1 (K2 ) 2
5) 1/(K1 )2K 2
2) II and III only
4) I, IV, and V only
5) 54
CO2(g) + SO2(g) « SO3(g) + CO(g)
The equilibrium expression for the reaction above at a
given temperature is 0.500. An equal number of moles
of carbon dioxide and sulfur dioxide are mixed at this
temperature, at a total pressure of 1.00 atm. What
percentage of sulfur dioxide is converted to product?
1) 91.6 %
3) 49.7 %
5) 60.2 %
55.
4) 27
I2(g) « 2 I(g) K = 9.0 moles/liter
At equilibrium, the concentration of “I 2” is 1.0
mole/liter. What is the concentration of the “I” at this
temperature if the system behaves according to the
above equation?
1) 9.0 moles/liter
3) 3.0 moles/liter
5) 6.0 moles/liter
54.
3) 12
2) (K1 ) 2K2
4) 1/K 1 (K2 ) 2
2 NO(g) + O2(g) « 2 NO2(g)
At 227ºC in a 2.00 L container there are 0.044 mol NO,
0.100 mol O 2 and 7.88 mol NO 2 at equilibrium. What
is the equilibrium constant if the system behaves
according to the above equation?
1) 3.2 × 10 4
3) 6.4 × 10 7
5) 3.2 × 10 10
2) 6.4 × 105
4) 3.2 × 10 8
Practice Questions
57.
H2(g) + I2(g) « 2 HI(g) Keq = 64
Equal moles of H 2 and I 2 are placed in a 1.00 L
container. At equilibrium, [HI] = 0.160 M. According
to the above equation, what is the initial [H2]?
1) 0.10 M
3) 0.30 M
5) 0.50 M
58.
59.
60.
left and Keq increases
left and Keq decreases
right and Keq increases
right and Keq decreases
right and Keq remains the same
2 B(s) + 3 F2(g) « 2 BF3(g)
The above equilibrium expression is
1)
2)
3)
4)
K trial > Keq and the [O 2] decreases
5)
Ktrial < Keq and the [O 2] decreases
Ktrial = Keq and the [O 2] decreases
shifts left and Keq value increases
shifts left and Keq value decreases
shifts right and K eq value increases
shifts right and K eq value decreases
shifts right and K eq value remains the same
C(s) + H2O(g) « CO(g) + H2(g)
The contents of a 1.00 L container at equilibrium were
analyzed and found to contain 0.20 mol C, 0.20 mol H2
O, 0.60 mol CO and 0.60 mol H 2. If the system
behaves like the equation above, the equilibrium
constant is
1) 0.11
61.
63.
Ktrial > Keq and the [O 2] increases
Ktrial < Keq and the [O 2] increases
PCl5(g) « PCl3(g) + Cl2(g) DH = +92.5 kJ
When the temperature decreases, the equilibrium
1)
2)
3)
4)
5)
1)
2)
3)
4)
5)
2) 0.20 M
4) 0.40 M
2 O3(g) « 3 O2(g) Keq = 55
If 0.060 mol of O 3 and 0.70 mol of O2 are introduced
into a 1.0 L vessel and the two molecules behave
according to the above equation, then
1)
2)
3)
4)
5)
62. For an exothermic reaction at equilibrium, an increase
in temperature will cause the equilibrium to shift
2) 0.56
3) 9.0
4) 11.2
5) 1.8
2 NH3(g) « N2(g) + 3 H2(g)
A flask is initially filled with NH 3. As the system
approaches equilibrium, the rate of the forward reaction
1) increases as the rate of the reverse reaction
decreases
2) decreases as the rate of the reverse reaction
increases
3) increases as the rate of the reverse reaction
increases
4) decreases as the rate of the reverse reaction
decreases
5) remains constant as the rate of the reverse reaction
decreases
64.
2 H2S(g) « 2 H2(g) + S2(g)
When the above reaction is at equilibrium, [H 2S] = 0.50
M, [H 2] = 0.10 M and [S 2] = 0.40 M. The value of K eq
is equivalent to which of the following?
1) (0.10)(0.40)
(0.50)
2) (0.50) (0.10)(0.40) 2
3) (0.50) (0.10)(0.50)
2 4) (0.50)
5) (0.10)2(0.40)
(0.50) 2
(0.40)(0.10) 2
Answer Key
Equilibrium Practice Questions
1.
2
37.
2
2.
2
38.
2
3.
2
39.
1
4.
1
40.
1
5.
4
41.
2
6.
5
42.
1
7.
4
43.
4
8.
2
44.
1
9.
5
45.
2
10.
1
46.
2
11.
3
47.
4
12.
1
48.
5
13.
3
49.
2
14.
2
50.
2
15.
4
51.
1
16.
2
52.
4
17.
5
53.
3
18.
3
54.
1
19.
4
55.
5
20.
1
56.
2
21.
5
57.
1
22.
1
58.
3
23.
3
59.
2
24.
1
60.
5
25.
2
61.
2
26.
2
62.
2
27.
3
63.
3
28.
1
64.
5
29.
4
30.
2
31.
1
32.
4
33.
5
34.
1
35.
1
36.
3