# Equilibrium Practice Test # 2 ANSWER KEY ```Equilibrium Practice Test # 2
1.
The slowest of the following reactions is:
A.
B.
C.
D.
2.
The rate of a chemical reaction is equal to the slope of the line with axes labelled
A.
B.
C.
D.
3.
Ag+(aq) + Cl-(aq) → AgCl(s)
H+(aq) + OH-(aq) → 2H2O(l)
3Ba2+(aq) + 2PO43-(aq) → Ba3(PO4)2(aq)
Cu(s) + 2Ag+(aq) → Cu2+(aq) + 2Ag(s)
x-axis
y-axis
time
mass
volume of gas
time
rate
time
time
concentration
Consider the following reaction: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + heat
The diagram that represents the relationship between rate and temperature is:
B.
A.
Rate
Rate
C.
D.
Temperature
Temperature
Rate
Rate
Temperature
Temperature
4.
Which of the following describes the energy of colliding particles as reacting molecules
approach each other?
A.
B.
C.
D.
KE
PE
decreases
increases
decreases
remains constant
increases
decreases
remains constant
increases
5.
The average kinetic energy per molecule can be increased by
A.
B.
6.
increasing temperature
increasing reactant concentration
increasing [H2]
decreasing the volume
C.
D.
finely powdering the C(s)
decreasing the temperature
Consider the following equilibrium: H2(g) + I2(g) ⇄ 2HI(g)
At equilibrium [H2] = 0.00220 M, [I2] = 0.00220 M, and [HI] = 0.0156 M
The value of the Keq is
A.
B.
8.
C.
D.
Consider the following reaction: C(s) + 2H2(g) ⇄ CH4(g) ΔH = -74.8 kJ
Which of the following will cause an increase in the value of the Keq?
A.
B.
7.
increasing pressure
3.10 x 10-4
1.99 x 10-2
C.
D.
5.03 x 101
3.22 x 103
Consider the rate diagram for the following reaction: 2HI(g) ⇄ H2(g) + I2(g)
forward
Rate
reverse
Time
t1
Which of the following occurs at t1?
A.
B.
9.
C.
D.
a decrease in volume
Chemical equilibrium is said to be dynamic because
A. the reaction proceeds quickly
B. the mass of the reactants is
decreasing
C. the macroscopic properties are constant
D. both forward and reverse rates are occurring
10.
11.
Which equation has the largest value of Keq?
A.
N2(g) + O2(g) ⇄ 2NO(g)
ΔH = 21 kJ
B.
C2H6(g) ⇄ 2C(s) + 3H2(g)
ΔH + 83 kJ
C.
H2(g) + 1/2O2(g) ⇄ H2O(g)
ΔH = -240 kJ
D.
Ca(s) + 3H2O(l) ⇄ Ca(OH)2(aq) + H2(g)
ΔH = -240 kJ
The value of the Keq can be changed by
A.
B.
12.
0.10
0.30
C.
D.
3.3
10
C.right because the Trial Keq &gt; Keq
D.right because the Trial Keq &lt; Keq
Given the following system: 2CrO42-(aq) + 2H+(aq) ⇄ Cr2O72-(aq) + H2O(l)
Which of the following chemicals, when added to the above system at equilibrium, would result
in a decrease in [Cr2O72-]?
A.
B.
15.
changing the reactant concentration
changing the volume of the container
Consider the following equilibrium: PCl3(g) + Cl2(g) ⇄ PCl5(g)
Keq = 2.30
A 1.0 L container is filled with 0.05 mole PCl5, 1.0 mole PCl3, and 1.0 mole Cl2. The system
proceeds to the
A.left because the Trial Keq &gt; Keq
B.left because the Trial Keq &lt; Keq
14.
C.
D.
Consider the following equilibrium: PCl3(g) + Cl2(g) ⇄ PCl5(g)
When 0.40 mole of PCl3 and 0.40 mole of Cl2 are placed in a 1.00 L container and allowed to
reach equilibrium, 0.244 mole of PCl5 are present. From this information, the value of the Keq is
A,
B.
13.
changing the temperature
NaOH
HNO3
C.
D.
What is the Keq expression for the following equilibrium?
3Fe(s) + 4H2O(g) ⇄ Fe3O4(s) + 4H2(g)
A.
B.
C.
D.
Keq = [H2]4
Keq = [H2]
[H2O]
Keq = [H2]4
[H2O]4
Keq = [Fe2O3][H2]4
[Fe][H2O]4
Na2CrO4
Na2Cr2O7
16.
Consider the following equilibrium: 2O3(g) ⇄ 3O2(g)
Keq = 65
Initially 0.10 mole of O3 and 0.10 mole of O2 are placed in a 1.0 L container, Which of the
following describes the changes in concentrations as the reaction proceeds towards equilibrium?
A.
B.
C.
D.
17.
[O2]
decreases
decreases
increases
increases
decreases
increases
decreases
increases
Consider the following equilibrium: 2CrO42-(aq) + 2H+(aq) ⇄ Cr2O72-(aq) + H2O(l)
yellow
orange
An unknown solution is added to an orange equilibrium system until the sample turns yellow.
The solution could be
A.
B.
18.
[O3]
KNO3
NaOH
C.
D.
NH4NO3
CH3COOH
Consider the following equilibrium:
CH3COOH(aq) ⇄ CH3COO-(aq) + H+(aq) + heat
A stress was applied at time t1 and the data plotted on the following graph:
The stress imposed at time t1 is the result of
[H+]
time
A.
B.
t1
decreasing the temperature
C.
D.
increasing the volume of the container
19.
Consider the following potential energy diagram for an equilibrium system:
P.E.
Progress of the reaction
When the temperature of the system is increased, the equilibrium shifts to the
A.
B.
20.
C.
D.
right and the Keq increases
right and the Keq decreases
Addition of a catalyst to an equilibrium system
A.
B.
C.
D.
21.
left and the Keq increases
left and the Keq decreases
increases the value of the Keq
increases the yield of the product
has no effect on the rates of the reaction
increases the rates of formation of both reactants and products
Ammonia, NH3, is produced by the following reaction:
N2(g) + 3H2(g) 
2NH3(g) + energy
Which of the following would result in the highest concentration of ammonia at equilibrium?
A.
B.
C.
D.
22.
increasing the temperature and increasing the pressure
decreasing the temperature and increasing the pressure
increasing the temperature and decreasing the pressure
decreasing the temperature and decreasing the pressure
Consider the following equilibrium:
2NO2(g)  N2O4(g)
Keq = 1.15
The equilibrium concentration of NO2 is 0.05mol/L. Calculate the equilibrium concentration of
N2O4(g).
A.
B.
0.22 mol/L
0.29 mol/L
C.
D.
0.43 mol/L
0.58 mol/L
23.
Consider the following equilibrium:
H2(g) + I2  2HI(g)
Keq = 50.0
What is the value Keq for the reaction rewritten as:
2HI(g)  H2(g) + I2(g)
A.
B.
24.
Keq = ?
-50.0
0.0200
C.
D.
25.0
50.0
Consider the following equilibrium: 2NOCl(g)  2NO(g) + Cl2(g)
A flask is filled with NOCl, NO, and Cl2(g). Initially there were a total of 5.0 moles of gases
present. When equilibrium is reached, there are a total of 8.0 moles of gases present. Which of
the following explains the observation?
A.
B.
C.
D.
25.
Consider the following equilibrium:
4NH3(g) + 5O2(g)  4NO(g) + 6H2O(g) + energy
Which of the following will cause the equilibrium to shift to the left?
A.
B.
26.
removing some NO(g)
C.
D.
increasing the volume
decreasing the temperature
A catalyst is added to a system already at equilibrium. How are the forward and reverse reaction
rates affected by the addition of the catalyst.
A.
B.
C.
D.
27.
The reaction shifted left because the Trial Keq &gt; Keq
The reaction shifted left because the Trial Keq &lt; Keq
The reaction shifted right because the Trial Keq &gt; Keq
The reaction shifted right because the Trial Keq &lt; Keq
Forward Rate
Reverse Rate
increases
increases
constant
constant
increases
constant
decreases
constant
Consider the following equilibrium: 2NOBr(g)  2NO(g) + Br2(g) Keq = 0.064
At equilibrium, a 1.00 L flask contains 0.030 mole NOBr and 0.030 mole NO. How many moles
of Br2 are present?
A.
B.
0.0019
0.064
C.
D.
0.030
0.47
28.
Which of the following does not apply to all chemical equilibrium systems?
A.
B.
C.
D.
29.
The relationship between Ea and reaction rate is best represented as
A.
C.
30.
B.
D.
The relationship between Keq and temperature for an exothermic reaction is best represented as
A.
C.
31.
They are closed.
The macroscopic properties are constant
Forward and reverse rates are equal
There are equal concentrations of reactants and products
B.
D.
The relationship between reaction rate and temperature is best represented by
A.
C.
B.
D.
32.
The relationship between Ea and temperature is best represented by
A.
B.
D.
C.
32.
Methanol, CH3OH, can be produced by the following:
CO(g) + 2H2(g)  CH3OH(g) + energy
The conditions necessary to maximize the equilibrium yield of CH3OH are
A.low temperature and low pressure
B.high temperature and low pressure
33.
low temperature and high pressure
high temperature and high pressure
Consider the following equilibrium: 2NO(g) + O2(g)  2NO2(g) + energy
When the volume of the container is increased, the equilibrium shifts to the
A.
B.
C.
D.
34.
C.
D.
left and the Keq decreases
right and the Keq increases
left and the Keq remains constant
right and the Keq remains comstant
Consider the following reaction:
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
H = -2202 kJ
Which of the following applies to the forward reaction?
A.
B.
C.
D.
Entropy
Enthalpy
increases
increases
decreases
decreases
increases
decreases
increases
decreases
Subjective
1.
Consider the following equilibrium:
N2H4(g) + 2O2(g)  2NO2(g) + 2H2O(g)
More oxygen is added to the above equilibrium. After the system re-establishes equilibrium,
identify the substance(s), if any, that have a net
2.
a)
increase in concentration
b)
decrease in concentration
Given the following equilibrium:
H2(g) + I2(g)
 2HI(g)
Initially, 0.200 mole H2 and 0.200 mole I2 were placed into a 1.0 L container. At equilibrium, the
[I2] is 0.040 M. Calculate the Keq.
3.
Consider the following equilibrium: 2CrO42-(aq) + 2H+(aq) ⇄ Cr2O72-(aq) + H2O(l)
yellow
orange
When HCl is added, the solution turns orange. Explain why this colour change occurs.
4.
Consider the following equilibrium system:
N2(g) + 3H2(g) 
2NH3(g) + energy
A 1.00 L container is filled with 7.0 mole NH3 and the system proceeds to equilibrium as
indicated by the graph.
8.0
M
6.0
4.0
2.0
NH3
a)
Draw and label the graph for N2 and H2. Fill in an ICE chart if you are not sure how to do this.
N2(g) + 3H2(g) 
2NH3(g)
I
C
E
b)
Calculate the Keq for the above reaction.
5.
Consider the following equilibrium 2NO(g) + O2(g)  2NO2(g)
Keq = 1.5
0.800 mole NO, 0.600 moles O2, and 0.400 moles NO2 are placed in a vessel that 2.0 L. Show by
calculation that the reaction is not at equilibrium? What will happen to [O2] as equilibrium is
approached?
6.
Consider the following equilibrium:
SO3(g) + NO(g)  NO2(g) + SO2(g) Keq = 0.500
Exactly 0.100 mole SO3 and 0.100 mole NO were placed in a 1.00 L flask and allowed to go to
equilibrium. Calculate the equilibrium concentration of SO2.
Equilibrium Practice Test # 2 ANSWER KEY
1.
The slowest of the following reactions is:
A.
B.
C.
D.
2.
The rate of a chemical reaction is equal to the slope of the line with axes labelled
A.
B.
C.
D.
3.
Ag+(aq) + Cl-(aq) → AgCl(s)
H+(aq) + OH-(aq) → 2H2O(l)
3Ba2+(aq) + 2PO43-(aq) → Ba3(PO4)2(aq)
Cu(s) + 2Ag+(aq) → Cu2+(aq) + 2Ag(s)
x-axis
y-axis
time
mass
volume of gas
time
rate
time
time
concentration
Consider the following reaction: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + heat
The diagram that represents the relationship between rate and temperature is:
B.
A.
Rate
Rate
C.
D.
Temperature
Temperature
Rate
Rate
Temperature
Temperature
4.
Which of the following describes the energy of colliding particles as reacting molecules
approach each other?
A.
B.
C.
KE
PE
decreases
increases
decreases
increases
decreases
remains constant
D.
5.
increasing [H2]
decreasing the volume
finely powdering the C(s)
decreasing the temperature
Consider the following equilibrium: H2(g) + I2(g) ⇄ 2HI(g)
At equilibrium [H2] = 0.00220 M, [I2] = 0.00220 M, and [HI] = 0.0156 M
The value of the Keq is
A.
B.
C.
D.
8.
increasing pressure
increasing temperature
increasing reactant concentration
Consider the following reaction: C(s) + 2H2(g) ⇄ CH4(g) ΔH = -74.8 kJ
Which of the following will cause an increase in the value of the Keq?
A.
B.
C.
D.
7.
increases
The average kinetic energy per molecule can be increased by
A.
B.
C.
D.
6.
remains constant
3.10
1.99
5.03
3.22
x
x
x
x
10-4
10-2
101
103
Consider the rate diagram for the following reaction: 2HI(g) ⇄ H2(g) + I2(g)
forward
Rate
reverse
Time
t1
Which of the following occurs at t1?
A.
B.
C.
D.
9.
a decrease in volume
Chemical equilibrium is said to be dynamic because
A.
B.
C.
D.
10.
11.
12.
Which equation has the largest value of Keq?
A.
N2(g) + O2(g) ⇄ 2NO(g)
ΔH = 21 kJ
B.
C2H6(g) ⇄ 2C(s) + 3H2(g)
ΔH + 83 kJ
C.
H2(g) + 1/2O2(g) ⇄ H2O(g)
ΔH = -240 kJ
D.
Ca(s) + 3H2O(l) ⇄ Ca(OH)2(aq) + H2(g)
ΔH = -240 kJ
The value of the Keq can be changed by
A.
B.
changing the temperature
C.
D.
changing the reactant concentration
changing the volume of the container
Consider the following equilibrium: PCl3(g) + Cl2(g) ⇄ PCl5(g)
When 0.40 mole of PCl3 and 0.40 mole of Cl2 are placed in a 1.00 L container and allowed to
reach equilibrium, 0.244 mole of PCl5 are present. From this information, the value of the Keq is
A,
B.
C.
D.
13.
the reaction proceeds quickly
the mass of the reactants is decreasing
the macroscopic properties are constant
both forward and reverse rates are occurring
0.10
0.30
3.3
10
Consider the following equilibrium: PCl3(g) + Cl2(g) ⇄ PCl5(g)
Keq = 2.30
A 1.0 L container is filled with 0.05 mole PCl5, 1.0 mole PCl3, and 1.0 mole Cl2. The system
proceeds to the
A.
B.
C.
D.
left because the Trial Keq &gt; Keq
left because the Trial Keq &lt; Keq
right because the Trial Keq &gt; Keq
right because the Trial Keq &lt; Keq
14.
Given the following system: 2CrO42-(aq) + 2H+(aq) ⇄ Cr2O72-(aq) + H2O(l)
Which of the following chemicals, when added to the above system at equilibrium, would result
in a decrease in [Cr2O72-]?
A.
NaOH
B.
HNO3
C.
D.
15.
Na2CrO4
Na2Cr2O7
What is the Keq expression for the following equilibrium?
3Fe(s) + 4H2O(g) ⇄ Fe3O4(s) + 4H2(g)
Keq = [H2]4
Keq = [H2]
[H2O]
Keq = [H2]4
[H2O]4
Keq = [Fe2O3][H2]4
[Fe][H2O]4
A.
B.
C.
D.
16.
Consider the following equilibrium: 2O3(g) ⇄ 3O2(g)
Keq = 65
Initially 0.10 mole of O3 and 0.10 mole of O2 are placed in a 1.0 L container, Which of the
following describes the changes in concentrations as the reaction proceeds towards equilibrium?
A.
B.
decreases
increases
decreases
increases
Consider the following equilibrium: 2CrO42-(aq) + 2H+(aq) ⇄ Cr2O72-(aq) + H2O(l)
yellow
orange
An unknown solution is added to an orange equilibrium system until the sample turns yellow.
The solution could be
KNO3
NaOH
C.
D.
18.
decreases
increases
increases
A.
B.
[O2]
decreases
C.
D.
17.
[O3]
NH4NO3
CH3COOH
Consider the following equilibrium:
CH3COOH(aq) ⇄ CH3COO-(aq) + H+(aq) + heat
A stress was applied at time t1 and the data plotted on the following graph:
The stress imposed at time t1 is the result of
[H+]
time
t1
A.
B.
C.
D.
19.
decreasing the temperature
increasing the volume of the container
Consider the following potential energy diagram for an equilibrium system:
P.E.
Progress of the reaction
When the temperature of the system is increased, the equilibrium shifts to the
A.
B.
C.
D.
20.
left and the Keq increases
left and the Keq decreases
right and the Keq increases
right and the Keq decreases
Addition of a catalyst to an equilibrium system
A.
B.
C.
increases the value of the Keq
increases the yield of the product
has no effect on the rates of the reaction
D.
increases the rates of formation of both reactants and products
21.
Ammonia, NH3, is produced by the following reaction:
N2(g) + 3H2(g) 
2NH3(g) + energy
Which of the following would result in the highest concentration of ammonia at equilibrium?
A.
increasing the temperature and increasing the pressure
B.
decreasing the temperature and increasing the pressure
C.
D.
22.
increasing the temperature and decreasing the pressure
decreasing the temperature and decreasing the pressure
Consider the following equilibrium:
2NO2(g)  N2O4(g)
Keq = 1.15
The equilibrium concentration of NO2 is 0.05 mol/L. Calculate the equilibrium concentration of
N2O4(g).
23.
A.
0.22 mol/L
B.
0.29 mol/L
C.
D.
0.43 mol/L
0.58 mol/L
Consider the following equilibrium:
H2(g) + I2  2HI(g)
Keq = 50.0
What is the value Keq for the reaction rewritten as:
2HI(g)  H2(g) + I2(g)
A.
B.
-50.0
0.0200
C.
D.
24.
Keq = ?
25.0
50.0
Consider the following equilibrium: 2NOCl(g)  2NO(g) + Cl2(g)
A flask is filled with NOCl, NO, and Cl2(g). Initially there were a total of 5.0 moles of gases
present. When equilibrium is reached, there are a total of 8.0 moles of gases present. Which of
the following explains the observation?
A.
B.
C.
The reaction shifted left because the Trial Keq &gt; Keq
The reaction shifted left because the Trial Keq &lt; Keq
The reaction shifted right because the Trial Keq &gt; Keq
D.
The reaction shifted right because the Trial Keq &lt; Keq
25.
Consider the following equilibrium:
4NH3(g) + 5O2(g)  4NO(g) + 6H2O(g) + energy
Which of the following will cause the equilibrium to shift to the left?
A.
B.
C.
D.
26.
A catalyst is added to a system already at equilibrium. How are the forward and reverse reaction
rates affected by the addition of the catalyst.
A.
B.
C.
D.
27.
increases
increases
constant
constant
increases
constant
decreases
constant
0.0019
0.064
0.030
0.47
They are closed.
The macroscopic properties are constant
Forward and reverse rates are equal
There are equal concentrations of reactants and products
The relationship between Ea and reaction rate is best represented as
A.
C.
30.
Reverse Rate
Which of the following does not apply to all chemical equilibrium systems?
A.
B.
C.
D.
29.
Forward Rate
Consider the following equilibrium: 2NOBr(g)  2NO(g) + Br2(g) Keq = 0.064
At equilibrium, a 1.00 L flask contains 0.030 mole NOBr and 0.030 mole NO. How many moles
of Br2 are present?
A.
B.
C.
D.
28.
removing some NO(g)
increasing the volume
decreasing the temperature
B.
D.
The relationship between Keq and temperature for an exothermic reaction is best represented as
A.
B.
31.
The relationship between reaction rate and temperature is best represented by
A.
C.
32.
D.
The relationship between Ea and temperature is best represented by
A.
C.
32.
B.
B.
D.
Methanol, CH3OH, can be produced by the following:
CO(g) + 2H2(g)  CH3OH(g) + energy
The conditions necessary to maximize the equilibrium yield of CH3OH are
A.
B.
C.
low temperature and low pressure
high temperature and low pressure
low temperature and high pressure
D.
33.
Consider the following equilibrium: 2NO(g) + O2(g)  2NO2(g) + energy
When the volume of the container is increased, the equilibrium shifts to the
A.
B.
C.
D.
34.
left and the Keq decreases
right and the Keq increases
left and the Keq remains constant
right and the Keq remains comstant
Consider the following reaction:
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
H = -2202 kJ
Which of the following applies to the forward reaction?
A.
B.
high temperature and high pressure
Entropy
Enthalpy
increases
increases
increases
C.
D.
decreases
decreases
decreases
increases
decreases
Subjective
1.
Consider the following equilibrium:
N2H4(g) + 2O2(g)  2NO2(g) + 2H2O(g)
More oxygen is added to the above equilibrium. After the system re-establishes equilibrium,
identify the substance(s), if any, that have a net
2.
a)
increase in concentration
NO
b)
decrease in concentration
N2H4
Given the following equilibrium:
H2 O
H2(g) + I2(g)
O2
 2HI(g)
Initially, 0.200 mole H2 and 0.200 mole I2 were placed into a 1.0 L container. At equilibrium, the
[I2] is 0.040 M. Calculate the Keq.
H2(g)
I
+
0.200 M
I2(g)
0.200 M

2HI(g)
0
3.
C
0.160 M
0.160 M
0.320 M
E
0.040 M
0.040 M
0.320 M
Keq
=
(0.320)2
(040)2
=
64
Consider the following equilibrium: 2CrO42-(aq) + 2H+(aq) ⇄ Cr2O72-(aq) + H2O(l)
yellow
orange
When HCl is added, the solution turns orange. Explain why this colour change occurs.
Adding HCl increases the [H+] and shifts the system right turning orange.
4.
Consider the following equilibrium system:
N2(g) + 3H2(g) 
2NH3(g) + energy
A 1.00 L container is filled with 7.0 mole NH3 and the system proceeds to equilibrium as
indicated by the graph.
H2
8.0
M
6.0
4.0
N2
2.0
NH3
a)
Draw and label the graph for N2 and H2. Fill in an ICE chart if you are not sure how to do
this.
N2(g)
I
C
0
3.0
+
3H2(g)
0
9.0

2NH3(g)
7.0
6.0
E
b)
3.0
1.0
Calculate the Keq for the above reaction.
Keq
5.
9.0
=
(1.0)2 =
(3.0)(9.0)3
0.00046
Consider the following equilibrium 2NO(g) + O2(g)  2NO2(g)
Keq = 1.5
0.800 mole NO, 0.600 moles O2, and 0.400 moles NO2 are placed in a vessel that 2.0 L. Show by
calculation that the reaction is not at equilibrium? What will happen to [O2] as equilibrium is
approached?
Trial Keq
(0.200)2
(0.400)2(0.300)
=
Not at equilibrium
6.
=
Shifts Right
0.833 &lt;
Keq = 1.5
[O2] will decrease.
Consider the following equilibrium:
SO3(g) + NO(g)  NO2(g) + SO2(g)
Keq = 0.500
Exactly 0.100 mole SO3 and 0.100 mole NO were placed in a 1.00 L flask and allowed to go to
equilibrium. Calculate the equilibrium concentration of SO2.
SO3(g) +
NO(g) 
NO2(g) +
SO2(g)
I
0.100
0.100
0
0
C
x
x
x
x
E
0.100 – x
0.100 – x
x
x
x2
(0.100 – x)2
=
0.500
x
0.100 – x
=
0.7071
1.7071x = 0.07071
x = 0.0414 M
[SO2] = 0.0414 M
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