110) The following picture represents the equilibrium state for the reaction A2 + B2 ⇌ 2AB.
What is the relationship between the rate constant for the forward reaction, kf, and the rate
constant for the reverse reaction kr?
A) kf < kr
B) kf = kr = 0
C) kf = kr
D) kf > kr
The reaction A2 + B2 ⇌ 2AB has an equilibrium constant Kc = 1.8. The following pictures
represent reaction mixtures that contain A2 molecules (shaded) and B2 molecules (unshaded),
and AB molecules.
111) Which nonequilibrium mixture will react in the forward direction to reach equilibrium?
A) reaction mixture (1)
B) reaction mixture (2)
C) reaction mixture (3)
D) reaction mixture (4)
112) Which nonequilibrium mixtures will react in the reverse direction to reach equilibrium?
A) reaction mixtures (1) and (2)
B) reaction mixtures (1) and (4)
C) reaction mixtures (2) and (3)
D) reaction mixtures (3) and (4)
The following pictures represent the initial state and the equilibrium state for the gaseous state
reaction of A2 molecules (shaded spheres) with B atoms (unshaded spheres) to give AB
molecules.
113) What is the best balanced chemical equation for the reaction?
A) A2 + B ⇌ A2B
B) 1A2 + 2 B ⇌ A2B2
C) A2 + 2 B ⇌ 2 AB
D) 6 A2 + 9 B ⇌ 3 A2 + 3B + 6 AB
114) If the volume of the equilibrium mixture is decreased, what will happen to the number of
AB molecules and the number of B atoms?
A) The number of AB molecules and the number of B atoms will both decrease.
B) The number of AB molecules will increase; the number of B atoms will decrease.
C) The number of AB molecules will decrease; the number of B atoms will increase.
D) The number of AB molecules and the number of B atoms will both increase.
Consider the reaction A + B ⇌ 2 AB. The vessel on the right contains an equilibrium mixture of
A atoms (shaded spheres), B atoms (unshaded spheres), and AB molecules.
115) If the barrier between the two vessels is removed and the contents of the two vessels are
allowed to mix, what will be observed?
A) The reaction will go in the forward direction decreasing the number of A atoms and B atoms
and increasing the number of AB molecules.
B) The reaction will go in the forward direction increasing the number of A atoms and B atoms
and decreasing the number of AB molecules.
C) The reaction will go in the reverse direction decreasing the number of A atoms and B atoms
and increasing the number of AB molecules.
D) The reaction will go in the reverse direction increasing the number of A atoms and B atoms
and decreasing the number of AB molecules.
Picture (1) represents the equilibrium mixture for the reaction A + B ⇌ 2 AB at 298 K.
116) If this reaction is exothermic, which picture (2)-(4) represents the equilibrium mixture at
400 K?
A) picture (2)
B) picture (3)
C) picture (4)
D) none of the above
117) If this reaction is endothermic, which picture (2)-(4) represents the equilibrium mixture at
400 K?
A) picture (2)
B) picture (3)
C) picture (4)
D) none of the above
118) Picture (1) represents the equilibrium mixture for the gas-phase reaction A + B ⇌ 2 AB at
298 K. If the volume of the equilibrium mixture is decreased, which picture (2)-(4) represents the
equilibrium at the reduced volume?
A) picture (2)
B) picture (3)
C) picture (4)
D) none of the above
Picture (1) represents an equilibrium mixture of solid CaCO3, solid CaO, and gaseous CO2,
obtained as a result of the endothermic decomposition of CaCO3.
119) Which picture (2)-(4) represents the equilibrium mixture after addition of four more CO2
molecules?
A) picture (2)
B) picture (3)
C) picture (4)
D) none of the above
120) Which picture (2)-(4) represents the equilibrium mixture at a higher temperature?
A) picture (2)
B) picture (3)
C) picture (4)
D) none of the above
121) Which picture (2)-(4) represents the equilibrium mixture when a catalyst is added?
A) picture (2)
B) picture (3)
C) picture (4)
D) all of the above
122) Which picture (2)-(4) represents the equilibrium mixture when more solid CaCO3 is added?
A) picture (2)
B) picture (3)
C) picture (4)
D) all of the above
123) Which picture (2)-(4) represents the equilibrium mixture when more solid CaO is added?
A) picture (2)
B) picture (3)
C) picture (4)
D) all of the above
13.2 Algorithmic Questions
1) For the reaction: N2(g) + 2 O2(g) ⇌ 2 NO2(g), Kc = 8.3 × 10-10 at 25°C. What is the
concentration of N2 gas at equilibrium when the concentration of NO2 is five times the
concentration of O2 gas?
A) 3.3 × 10-11 M
B) 1.7 × 10-10 M
C) 6.0 × 109 M
D) 3.0 × 1010 M
2) The decomposition of ammonia is: 2 NH3(g) = N2(g) + 3 H2(g). If Kp is 1.5 × 103 at 400°C,
what is the partial pressure of ammonia at equilibrium when N2 is 0.10 atm and H2 is 0.15 atm?
A) 2.2 × 10-7 atm
B) 4.7 × 10-4 atm
C) 2.1 × 103 atm
D) 4.4 × 106 atm
3) The equilibrium constant is equal to 5.00 at 1300 K for the reaction:
2 SO2(g) + O2(g) ⇌ 2 SO3(g).
If initial concentrations are [SO2] = 6.00 M, [O2] = 0.45 M, and [SO3] = 9.00 M, the system is
A) at equilibrium.
B) not at equilibrium and will remain in an unequilibrated state.
C) not at equilibrium and will shift to the left to achieve an equilibrium state.
D) not at equilibrium and will shift to the right to achieve an equilibrium state.
4) The equilibrium constant, Kp, equals 3.40 at 25°C for the isomerization reaction:
cis-2-butene ⇌ trans-2-butene.
If a flask initially contains 5.00 atm of each gas, in what direction will the system shift to reach
equilibrium?
A) It will shift left.
B) It will shift right.
C) The system is already at equilibrium.
D) The system is not at equilibrium and will remain in an unequilibrated state.
5) Cyclohexane (C6H12) undergoes a molecular rearrangement in the presence of AlCl3 to form
methylcyclopentane (MCP) according to the equation:
C6H12 ⇌ MCP
If Kc = 0.143 at 25°C for this reaction, predict the direction in which the system will shift if the
initial concentrations of C6H12 and MCP are 0.0400 M and 0.0200 M, respectively. The system
A) will shift left.
B) will shift right.
C) is already at equilibrium.
D) is not at equilibrium and will remain in an unequilibrated state.
6) At a certain temperature, nitrogen and hydrogen react to form ammonia:
N2(g) + 3 H2(g) ⇌ 2 NH3(g).
When initial amounts of N2, H2, and NH3 are mixed, the concentration of NH3 increases.
Which statement below is true?
A) Kc < Q
B) Kc > Q
C) Kc = Q
D) More information is needed to make a statement about Kc.
7) An equilibrium mixture of CO, O2 and CO2 at a certain temperature contains 0.0010 M CO2
and 0.0100 M O2. At this temperature, Kc equals 1.4 × 102 for the reaction:
2 CO(g) + O2(g) ⇌ 2 CO2(g).
What is the equilibrium concentration of CO?
A) 7.1 × 10-7 M
B) 8.4 × 10-4 M
C) 1.4 × 10-2 M
D) 1.2 × 10-1 M
8) The equilibrium constant, , is equal to 2.00 at 1000° C for the reaction:
2CO (g) ⇌ C (g) + C (g)
If 0.079moles of C and 0.079 moles of C are introduced into a 1.0-L flask, what will be the
concentration of CO when equilibrium is reached?
A) 0.041 M
B) 0.058 M
C) 0.021 M
D) 0.025 M
9) The equilibrium constant, , is equal to 2.00 at 1000° C for the reaction:
2CO (g) ⇌ C (g) + C (g)
If 2.0 moles of CO is introduced into in a 1.0-L flask, what will be the concentration of C
when equilibrium is reached?
A) 0.74 M
B) 0.52 M
C) 1.01 M
D) 0.78 M
10) The equilibrium constant, , is equal to 1.4 at 1200° K for the reaction:
C (g) + (g) ⇌ CO(g) + O(g)
If 0.75 moles of C and 0.75 moles of are introduced into a 1.0-L flask, what will be the
concentration of C when equilibrium is reached?
A) 0.34 M
B) 0.41 M
C) 0.44 M
D) 0.51M
11) The equilibrium constant, , is equal to 1.4 at 1200° K for the reaction:
C (g) + (g) ⇌ CO(g) + O(g)
If 0.65 moles of C and 0.65 moles of are introduced into a 1.0-L flask, what will be the
concentration of CO when equilibrium is reached?
A) 0.30 M
B) 0.35 M
C) 0.38 M
D) 0.42M
12) The equilibrium constant, , is equal to 1.4 at 1200° K for the reaction:
C (g) + (g) ⇌ CO(g) + O(g)
If 0.50 moles of C and 0.60 moles of are introduced into a 1.0-L flask, what will be the
concentration of C when equilibrium is reached?
A) 0.30 M
B) 0.21 M
C) 0.35 M
D) 0.55M
13) The equilibrium constant, , is equal to 1.4 at 1200° K for the reaction:
C (g) + (g) ⇌ CO(g) + O(g)
If 0.50 moles of C and 0.60 moles of are introduced into a 1.0-L flask, what will be the
concentration of CO when equilibrium is reached?
A) 0.30 M
B) 0.21 M
C) 0.35 M
D) 0.55M
14) At a certain temperature, Kc equals 1.4 × 102 for the reaction:
2 CO(g) + O2(g) ⇌ 2 CO2(g).
If a 3.00-L flask contains 0.400 mol of CO2 and 0.100 mol of O2 at equilibrium, how many
moles of CO are also present in the flask?
A) 0.555 mol
B) 0.185 mol
C) 0.107 mol
D) 0.0114 mol
15) For the isomerization reaction:
butane ⇌ isobutane
Kp equals 25 at 500°C. If the initial pressures of butane and isobutane are 20. atm and 0.0 atm,
respectively, what are the pressures of the two gases at equilibrium?
A) P(butane) = 0.77 atm and P(isobutane) = 19.2 atm
B) P(butane) = 0.80 atm and P(isobutane) = 20. atm
C) P(butane) = 19.2 atm and P(isobutane) = 0.77 atm
D) P(butane) = 20 atm and P(isobutane) = 0.80 atm
16) Cyclohexane, C6H12, undergoes a molecular rearrangement in the presence of AlCl3 to
form methylcyclopentane, CH3C5H9, according to the equation:
C6H12 ⇌ CH3C5H9
If Kc = 0.143 at 25°C for this reaction, find the equilibrium concentrations of C6H12 and
CH3C5H9 if the initial concentrations are 0.200 M and 0.075 M, respectively.
A) [C6H12] = 0.041 M, [CH3C5H9] = 0.041 M
B) [C6H12] = 0.159 M, [CH3C5H9] = 0.116 M
C) [C6H12] = 0.241 M, [CH3C5H9] = 0.034 M
D) [C6H12] = 0.253 M, [CH3C5H9] = 0.022 M
17) At a certain temperature the equilibrium constant, Kc, equals 0.11 for the reaction:
2 ICl(g) ⇌ I2(g) + Cl2(g).
What is the equilibrium concentration of ICl if 0.75 mol of I2 and 0.75 mol of Cl2 are initially
mixed in a 2.0-L flask?
A) 0.22 M
B) 0.28 M
C) 0.45 M
D) 0.56 M
18) The equilibrium constant, Kp, equals 3.40 for the isomerization reaction:
cis-2-butene ⇌ trans-2-butene.
If a flask initially contains 0.250 atm of cis-2-butene and 0.145 atm of trans-2-butene, what is
the equilibrium pressure of each gas?
A) P(cis-2-butene) = 0.0426 atm and P(trans-2-butene) = 0.145 atm
B) P(cis-2-butene) = 0.0471 atm and P(trans-2-butene) = 0.160 atm
C) P(cis-2-butene) = 0.0735 atm and P(trans-2-butene) = 0.250 atm
D) P(cis-2-butene) = 0.0898 atm and P(trans-2-butene) = 0.305 atm
19) Phosphorus pentachloride decomposes to phosphorus trichloride at high temperatures
according to the equation:
At 250° 0.125 M PCl5 is added to the flask. If Kc = 1.80, what are the equilibrium
concentrations of each gas?
A) [PCl5] = 0.00765 M, [PCl3] = 0.117 M, and [Cl2] = 0.117 M
B) [PCl5] = 0.0625 M, [PCl3] = 0.335 M, and [Cl2] = 0.335 M
C) [PCl5] = 1.80 M, [PCl3] = 1.80 M, and [Cl2] = 1.80 M
D) [PCl5] = 3.96 M, [PCl3] = 3.83 M, and [Cl2] = 3.83 M
20) Kc is 1.67 × 1020 at 25°C for the formation of iron(III) oxalate complex ion:
Fe3+(aq) + 3 C2O42-(aq) ⇌ [Fe(C2O4)3]3-(aq).
If 0.0400 M Fe3+ is initially mixed with 1.00 M oxalate ion, what is the concentration of Fe3+
ion at equilibrium?
A) 3.51 × 10-22 M
B) 0.0100 M
C) 4.18 × 1017 M
D) 2.85 × 1021 M
13.3 Short Answer Questions
1) A reaction in which reactants form products in the forward reaction and products
simultaneously form reactants in the reverse reaction is said to be ________.
2) In a reversible reaction, when the rate of the forward reaction equals the rate of the reverse
reaction, the reaction is at ________.
3) For the reaction shown below, N2O4 and NO2 have equilibrium concentrations, [N2O4]eq =
2.160 × 10–4 and [NO2]eq = 1.001 × 10–3, respectively. The equilibrium constant, Kc, for this
reaction equals ________.
N2O4(g) ⇌ 2 NO2(g)
4) For the reaction shown below the value of Kp is ________ than the value of Kc, because △n =
________.
N2O4(g) ⇌ 2 NO2(g)
5) For the reaction shown below the equilibrium constant expression for Kc = ________.
HF(aq) + H2O(l) ⇌ H3O+(aq) + F–(aq)
6) Kc = 57.0 at 700 K for the reaction shown below.
H2(g) + I2(g) ⇌ 2 HI(g)
If [H2(g)] = [I2(g)] = 0.200 M at equilibrium, the molar concentration [HI((g)] = ________ at
equilibrium.
7) Kc = 1.2 × 10–42 at 500 K for the reaction shown below.
H2(g) ⇌ 2 H(g)
If [H2] = 1 × 10–2 M and [H] = 1.2 × 10–22 M, in order to achieve equilibrium a net reaction
must occur from ________ to ________ until Qc = ________.
8) If additional SCN– is added to the equilibrium system shown below, Le Châtelier’s principle
predicts a net reaction from ________ to ________, causing the red color to become ________.
Fe3+(aq) + SCN–(aq) ⇌ FeSCN2+(aq)
yellow colorless red
9) According to Le Châtelier’s principle, if the volume of the vessel containing the equilibrium
system shown below is decreased, there will be an increase in the concentration of ________ and
a decrease in the concentration of ________.
H2(g) ⇌ 2 H(g)
10) The reaction below is heated from 20°C to 90°C, according to Le Châtelier’s principle, there
will be a net reaction from ________ to ________, and the brown color will become ________.
N2O4(g) ⇌ 2 NO2(g) △H°= + 57.2 kJ
colorless brown