chem. equilibrium
TRANSCRIPT
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Topic11 Chemical Equilibrium
Part A Unit-based exercise
Unit 39 An introduction tochemical equilibrium
Fill in the blanks
1 Chemical reaction that take place in one direction
only are known as irreversible reactions.
2 The reaction between ethanoic acid and ethanol
does not go to completion no matter how long
the reaction mixture is heated under reflux. This
is known as a reversible reaction.
3 A dynamic equilibrium is reached when
the forward and backward reactions occur at the
same rate.
4 In an aqueous solution of potassium chromate,
the following equilibrium system is established:
2CrO42
(aq) + 2H+(aq) Cr2O7
2(aq) + H2O(l)
a) When a little dilute sulphuric acid is added to
the system, the colour of the solution changes
from yellow to orange . This
indicates that the concentration of Cr2O72
(aq)
ions has increased while the concentration
of CrO42
(aq) ions has decreased.
b) When a little dilute sodium hydroxide solution
is added to the resulting solution, the colour
of the solution changes from orange
to yellow . This indicates that the
concentration of CrO 42
(aq) ions
has increased while the concentration
of Cr2O72
(aq) ions has decreased.
5 The direction in which a net reaction will proceed
to achieve equilibrium can be predicted by
comparing reaction quotient (Qc) and equilibrium
constant (Kc).
a) When Qc < Kc, a net forward reaction
must occur until equilibrium is reached.
b) When Qc > Kc, a net backward reaction
must occur until equilibrium is reached.
True or false
Decide whether each of the following statements is
true or false.
6 A dynamic equilibrium is reached when T
the forward and backward reactions occur
at the same rate.
7 For a system at equilibrium, the Fconcentrations of the reactants and the
products must be the same.
8 Equilibrium can only be established in an F
open system.
9 The value of Kc for a reaction can be F
used to judge the rate at which
equilibrium is attained.
10 If Qc is greater than Kc, the system is not Tat equilibrium.
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Multiple choice questions
11 Which of the following statements is true for a
reaction system at equilibrium?
A All reactions cease.
B The reactions have gone to completion.
C The rates of the forward and backward
reactions are equal.
D The amount of products equals the amount
of reactants. C
12 Consider the following reaction:
2SO3(g) 2SO2(g) + O2(g)
Initially, SO3(g) is placed in an empty flask. How do
the rates of the forward and backward reactions
change as the system proceeds to equilibrium?
Forward Backward
reaction rate reaction rate
A Increases increases
B Increases decreases
C Decreases decreases
D Decreases increases D
13 Consider the following equilibrium system:
2NH3(g) N2(g) + 3H2(g)
Which of the following graphs represents [H2(g)]after equilibrium has been established?
5JNF
A
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B
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C
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D
B
14 Two experiments were performed involving the
following equilibrium. The temperature was the
same in both experiments.
H2(g) + I2(g) 2HI(g)
In experiment A, 1.00 mol dm3
H2(g) and 1.00
mol dm3
I2(g) were initially added to a flask and
equilibrium was established. In experiment B, 2.00
mol dm3
HI(g) were initially added to a second
flask and equilibrium was established. Which of
the following statements is always true about the
equilibrium concentrations?
A [H2(g)] equals [HI(g)] in experiment A.
B [HI(g)] equals 2[H2(g)] in experiment A.
C [HI(g)] in experiment A equals [HI(g)] in
experiment B.
D [HI(g)] in experiment A equals1
2[I2(g)] in
experiment B. C
15 Which of the factors below is NOT a condition
necessary for equilibrium?
A A closed system
B A constant temperature
C Equal forward and backward reaction rates
D Equal concentrations of reactants and
products D
Directions: Questions 16 and 17 refer to the followinginformation.
Consider the following reaction:
2NH3(g) N2(g) + 3H2(g)
A 1.00 dm3
container is initially filled with NH3(g).
16 What are the changes in the rate of the forward
reaction and the concentration of N2(g) as the
system approaches equilibrium?
Rate of
forward reaction Concentration of N2(g)
A Decreases increases
B Decreases decreases
C Increases increases
D Increases decreases A
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17 At equilibrium, there is 0.0400 mole of N2(g)
present. What is the concentration of H2(g)?
A 0.0400 mol dm3
B 0.0600 mol dm3
C 0.0800 mol dm3
D 0.120 mol dm3
D
18
5JNF
$PODFOUSBUJPO
Which of the following chemical reactions isconsistent with the above graph?
A X(g) Y(g) + 2Z(g)
B X(g) Y(g) + 3Z(g)
C 2X(g) Y(g) + Z(g)
D 2X(g) 2Y(g) + Z(g) B
19 Consider the hypothetical reaction:
2A(g) + B(g) 3C(g)
What is the equilibrium constant, Kc?
A Kc =[C(g)]3
[A(g)]2[B(g)]
B Kc =[A(g)]
2[B(g)]
[C(g)]3
C Kc =[C(g)]
3
[A(g)]2
+ [B(g)]
D Kc =[A(g)]
2+ [B(g)]
[C(g)]3
A
20 What is the equilibrium constant, Kc, for the
reaction below?
2S(s) + 3O2(g) 2SO3(g)
A Kc =2[SO3(g)]
2[S(s)] + 3[O2(g)]
B Kc =2[SO3(g)]
3[O2(g)]
C Kc =[SO3(g)]
2
[S(s)]2[O2(g)]
3
D Kc =[SO3(g)]
2
[O2(g)]3
D
21 CO2(g) + 3H2(g) CH3OH(g) + H2O(g)
What is the equilibrium constant, Kc, for this
reaction?
A Kc =[CH3OH(g)][H2O(g)]
[CO2(g)][H2(g)]3
B Kc =[CO2(g)][H2(g)]
3
[CH3OH(g)][H2O(g)]
C Kc =[CH3OH(g)] + [H2O(g)]
[CO2(g)] + 3[H2(g)]
D Kc =[CO2(g)] + 3[H2(g)]
[CH3OH(g)] + [H2O(g)] A
22 Consider the following equilibrium system:
CaCO3(s) + 2HF(g)
CaF2(s) + H2O(g) + CO2(g)
Which of the following expressions represents the
equilibrium concentration of CO2(g)?
A [CO2(g)] =Kc[H2O(g)]
[HF(g)]2
B [CO2(g)] =Kc[HF(g)]
2
[H2O(g)]
C [CO2(g)] =Kc[CaCO3(s)][HF(g)]
2
[H2O(g)]
D [CO2(g)] =Kc[CaCO3(s)][HF(g)]
2
[CaF2(s)][H2O(g)] B
23 For which of the following systems does Kc =[O2(g)]?
A O2(l) O2(g)
B 3O2(g) 2O3(g)
C 2O2(g) + N2(g) N2O4(g)
D 2Hg(s) + O2(g) 2HgO(s) A
24 1 mole of N2O4(g) was placed in an empty 1 dm3
container and allowed to reach equilibrium
according to the following equation:
N2O4(g) 2NO2(g)At equilibrium, xmole of N2O4(g) had dissociated.
What is the value of the equilibrium constant, Kc,
at the temperature of the experiment?
A2x
(1 x)B
2x
(1 x)2
C4x
2
(1 x)2
D4x
2
(1 x) D
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25 An equilibrium mixture at constant temperature
and pressure,
SO3(g) + NO(g) SO2(g) + NO2(g)
was analyzed and found to contain 0.0800 mole
of SO2(g), 0.200 mole of NO2(g), 0.250 mole of
NO(g) and 0.480 mole of SO3(g) in a 10.0 dm3
container. What is the equilibrium constant, Kc,
for this reaction?
A 7.52
B 1.14
C 0.302
D 0.133 D
26 The reaction below reaches equilibrium in a closed
reaction vessel of volume 2.50 dm3.
2NO(g) + O2(g) 2NO2(g)
At equilibrium, there are 2.83 moles of NO(g),
3.00 moles of O2(g), and 18.0 moles of NO2(g).
What is the equilibrium constant, Kc, for the
reaction?
A 0.218 dm3
mol1
B 1.83 dm3
mol1
C 13.4 dm3
mol1
D 33.7 dm3
mol1
D
27 NO(g) and CO2(g) react according to the following
equation:
NO(g) + CO2(g) NO2(g) + CO(g)
In an experiment, 4.00 moles of NO(g) and 0.900
mole of CO2(g) are placed in a 2.00 dm3
reaction
vessel.
At equilibrium, 0.100 mole of CO2(g) is present.
What is the equilibrium constant, Kc, for the
reaction?
A 0.500
B 1.60C 2.00
D 5.00 C
Directions: Questions 28 and 29 refer to the following
information.
2.00 moles of each of H2(g) and I2(g) are allowed to
react in a 1.00 dm3
container at a certain temperature.
3.50 moles of HI(g) are present at equilibrium.
28 What is the value of the equilibrium constant,Kc?
A 5.10 x 103
B 3.74
C 56.0
D 196 D
29 Which of the following graphs shows how the
rates of the forward and backward reactions
change when hydrogen and iodine are mixed?
3BUF
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GPSXBSESFBDUJPO
CBDLXBSESFBDUJPO
LFZ
A
3BUF
5JNF
B
3BUF
5JNF
C
3BUF
5JNF
D
A
30 X2(g) and Y2(g) react according to the following
equation:
X2(g) + Y2(g) 2XY(g)
A mixture containing 4.00 moles each of X2(g)
and Y2(g) is heated in a closed container. The
system is allowed to reach equilibrium. The graph
shows how the number of moles of each gas
varies with time.
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5JNF
9HBOE:H
9:H
/VNCFSPGNPMFT
What is the equilibrium constant, Kc, for the
reaction?
A 0.0278
B 0.167
C 6.00
D 36.0 D
31 Consider the following reaction:
Fe3+(aq) + SCN(aq) [Fe(SCN)]2+(aq)
50.0 cm3
of 0.100 mol dm3
Fe3+
(aq) are added
to 30.0 cm3
of 0.200 mol dm3
SCN(aq). At
equilibrium, the concentration of [Fe(SCN)]2+
(aq)
is found to be 0.0500 mol dm3
.
What is the equilibrium constant, Kc, for the
reaction?
A 6.25 x 103
dm3
mol1
B 0.400 dm3
mol1
C 2.50 dm
3
mol
1
D 160 dm3
mol1
D
Directions: Questions 32 and 33 refer to the following
information.
Equal volumes of two 1.00 mol dm3
solutions of
W and X are mixed. The reaction rapidly reaches
equilibrium.
W(aq) + X(aq) Y(aq) + Z(aq)
The concentration of Z(aq) is found to be 0.300
mol dm3
.
32 What is the equilibrium concentration of
W(aq)?
A 0.100 mol dm3
B 0.200 mol dm3
C 0.500 mol dm3
D 0.700 mol dm3
B
33 What is the value of Kc for the reaction?
A 9.00
B 2.25
C 0.360
D 0.184 B
34 PCl5(g) decomposes to form PCl3(g) and Cl2(g)according to the equation:
PCl5(g) PCl3(g) + Cl2(g)
Four different flasks, A, B, C and D, at the same
temperature, contain a mixture of PCl5(g), PCl3(g)
and Cl2(g). The concentration, in mol dm3
, of
these components in each of the flasks is shown
below. In three of the four flasks, the mixture of
gases is at equilibrium.
In which one is the mixture of gases NOT at
equilibrium?
[PCl5(g)] [PCl3(g)] [Cl2(g)]
A 0.10 0.40 0.10
B 0.15 0.20 0.30
C 0.20 0.30 0.15
D 0.30 0.60 0.20 C
35 For which system does the equilibrium constant,
Kc, have units of dm3
mol1
?
A H2(g) + I2(g) 2HI(g)
B 2NO2(g) N2O4(g)
C 2SO3(g) 2SO2(g) + O2(g)
D CH3COOC2H5(l) + H2O(l)
CH3COOH(l) + C2H5OH(l) B
36 For which system does the equilibrium constant,
Kc, have NO units?
A C(s) + H2O(g) CO(g) + H2(g)
B SO3(g) + NO(g) SO2(g) + NO2(g)
C Cu2+
(aq) + 4NH3(aq) [Cu(NH3)4]2+
(aq)
D N2O4(g) 2NO2(g) B
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37 The equilibrium constant, Kc, for the reaction
N2O4(g) 2NO2(g)
is 6.10 x 103
mol dm3
at 25 C. What is the
Kc for the following reaction?
NO2(g)1
2
N2O4(g)
A 327 dm3
2 mol
1
2
B 164 dm3
2 mol
1
2
C 12.8 dm3
2 mol
1
2
D 3.05 x 103
dm3
2 mol
1
2 C
38 Consider the following hypothetical equilibrium
systems:
A(g) B(g) Kc = 2.00
B(g) C(g) Kc = 0.0100
What is the value of Kc for the following
reaction?
2C(g) 2A(g)
A 2 500
B 200
C 50.0
D 4.00 x 104
A
39 Starting with equal concentrations of reactants,
which of the following will be closest to
completion at equilibrium?
A CO(g) + Cl2(g) COCl2(g) Kc = 22
B 2H2O(g) + 2Cl2(g) 4HCl(g) + O2(g)
Kc = 5.0 x 104
C 2HBr(g) H2(g) + Br2(g)
Kc = 7.0 x 1020
D N2(g) + O2(g) 2NO(g)
Kc = 1.0 x 1031
A
40 An equal number of moles of methane and steamare placed in a closed container at 800 C. The
following reaction occurs.
CH4(g) + H2O(g) CO(g) + 3H2(g)
Kc = 1.78 x 103
at 800 C
Which of the following is correct at equilibrium
at this temperature?
A [CO(g)] > [CH4(g)]
B [CH4(g)] > [H2(g)]
C [CH4(g)] = [CO(g)]
D [CO(g)] = 3[H2(g)] B
41 At a particular temperature, the equilibrium
constant, Kc, for the reaction below is 65.0
dm3
mol1
.
2NO(g) + O2(g) 2NO2(g)
At equilibrium, the concentration of NO(g) is 0.600
mol dm3
and that of O2(g) is 0.300 mol dm3
.
What is the equilibrium concentration of
NO2(g)?
A 19.0 mol dm3
B 3.44 mol dm3
C 2.65 mol dm3
D 0.526 mol dm3 C
42 1.50 moles of CS2(g) and 3.00 moles of Cl2(g)
are mixed and the following equilibrium is
established:
CS2(g) + 3Cl2(g) S2Cl2(g) + CCl4(g)
At equilibrium, 0.300 mole of CCl4(g) is found.
How much Cl2(g) is present?
A 0.900 mole
B 1.80 moles
C 2.10 moles
D 2.70 moles C
43 At a certain temperature, the equilibrium constant,
Kc, for the reaction
2NH3(g) + Cl2(g) N2H4(g) + 2HCl(g)
is 4.00.
An equilibrium mixture in a 1.00 dm3
container
has 2.60 moles of NH3(g), 4.00 moles of Cl2(g)
and 5.90 moles of N2H4(g).
What is the equilibrium concentration of
HCl(g)?
A 4.28 mol dm3
B 5.34 mol dm3
C 10.7 mol dm3
D 12.0 mol dm3
A
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44 When 1.00 mole of phosphorus pentachloride
was heated to 523 K in a closed vessel, 50.0%
dissociated as shown.
PCl5(g) PCl3(g) + Cl2(g)
How many moles of gas were present in the
equilibrium mixture?
A 0.50
B 1.00
C 1.50
D 2.00 C
45 Consider the following reaction:
2NOCl(g) 2NO(g) + Cl2(g)
Initially, some NOCl(g) was placed in a 1.00 dm3
container. At equilibrium, there were 0.860 mole
of NOCl(g), 0.0300 mole of NO(g) and 0.0150mole of Cl2(g). How many moles of NOCl(g) were
initially added to the container?
A 0.785 mole
B 0.815 mole
C 0.890 mole
D 0.905 mole C
46 Consider the following equilibrium system:
2O3(g) 3O2(g) Kc = 1
Which of the following correctly compares theequilibrium concentrations of the two species?
A [O3(g)] = [O2(g)]
B [O3(g)] = [O2(g)]3
2
C [O3(g)] = [O2(g)]2
3
D [O3(g)]3
2 = [O2(g)] B
47 Consider the following equilibrium system:
N2O4(g) 2NO2(g) Kc = 4.50
Initially, 0.500 mole of N2O4(g) and 0.500 mole
of NO2(g) are placed in a 1.00 dm3
container.
Which of the following describes the changes in
concentrations as the system proceeds towards
equilibrium?
[N2O4(g)] [NO2(g)]
A Decreases decreases
B Decreases increases
C Increases decreases
D Increases increases B
48 Consider the following reaction:
2SO2(g) + O2(g) 2SO3(g)
In an experiment, 0.10 mole of O2(g) and 0.10
mole of SO3(g) are added to an empty 1.0 dm3
flask and then the flask is sealed. The reaction
goes backward to establish equilibrium. Which
of the following must be true at equilibrium?
A [SO2(g)] = [O2(g)] = [SO3(g)]
B [O2(g)] < [SO3(g)]
C [O2(g)] = [SO2(g)]
D [SO3(g)] < [O2(g)] D
49 Propanone can be made from propan-2-ol.
C3H8O(g) C3H6O(g) + H2(g) Kc = 0.0100
In an experiment, 6.00 moles of C3H8O(g), 0.150
mole of C3H6O(g) and 0.100 mole of H2(g) areplaced in a 1.00 dm3
container and allowed to
establish equilibrium.
Which of the following change(s) will occur as
the system proceeds towards equilibrium?
A [C3H6O(g)] increases while [H2(g)] decreases.
B [C3H6O(g)] and [H2(g)] both increase.
C [C3H8O(g)] and [H2(g)] both increase.
D [C3H8O(g)] and [C3H6O(g)] both decrease. B
50 Consider the following reaction:
3NO2(g) N2O5(g) + NO(g)
Kc = 1.0 x 1011
dm3
mol1
Initially, some NO2(g), N2O5(g) and NO(g) are placed
in a container and allowed to reach equilibrium.
When equilibrium is established, it is found that
the pressure has increased. Which of the following
combinations is correct as the system proceeds
towards equilibrium?
Reaction Direction
quotient Qc of net reaction
A Qc > Kc net forward reaction
B Qc < Kc net forward reaction
C Qc > Kc net backward reaction
D Qc < Kc net backward reaction C
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Directions: Questions 51 and 52 refer to the following
information.
The equilibrium constant for the following reaction is
Kc = 2.50 x 104
at 25 C.
N2(g) + C2H2(g) 2HCN(g)
In an experiment, a mixture of N2(g), C2H2(g) andHCN(g), all of initial concentrations 1.00 mol dm
3,
are allowed to reach equilibrium.
51 Which of the following statements is correct as
the system proceeds towards equilibrium?
A A net forward reaction occurs because Qc
Kc.D A net backward reaction occurs because Qc
> Kc. D
52 What is the concentration of HCN(g) at
equilibrium?
A 0.0158 mol dm3
B 0.0235 mol dm3
C 1.28 mol dm3
D 1.53 mol dm3
B
53 Consider the following:
(1) Constant temperature
(2) Equal concentrations of reactants and
products
(3) Equal rates of forward and backward
reactions
A system at equilibrium must have
A (1) and (2) only
B (1) and (3) only
C (2) and (3) onlyD (1), (2) and (3) B
54 Consider the following reaction:
2ICl(g) I2(g) + Cl2(g)
Initially, some ICl(g) is placed in an empty flask.
Which of the following statements describe(s)
the change(s) occurring as the system proceeds
towards equilibrium?
(1) The rate of the backward reaction
increases.
(2) Concentration of ICl(g) increases.
(3) Concentration of Cl2(g) increases.
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only C
55 Consider the following reaction:
2SO2(g) + O2(g) 2SO3(g) Kc = 4.00
In an experiment, 0.600 mole of SO2(g), 0.300
mole of O2(g) and 0.600 mole of SO3(g) are placed
in a 1.00 dm3
container. The system is allowed
to reach equilibrium. Which of the following are
correct as the system approaches equilibrium?
(1) Concentration of SO2(g) increases.
(2) Concentration of O2(g) decreases.
(3) Concentration of SO3(g) increases.
A (1) and (2) onlyB (1) and (3) only
C (2) and (3) only
D (1), (2) and (3) C
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Directions : Each question (Questions 56 60) consists of two separate statements. Decide whether each
of the two statements is true or false; if both are true, then decide whether or not the second
statement is a correct explanation of the first statement. Then select one option from A to D
according to the following table :
A Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
B Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.C The 1st statement is false but the 2nd statement is true.
D Both statements are false.
1st statement 2nd statement
56 All equilibrium systems have equal concentrations At equilibrium, the rate of the forward C
of reactants and products. reaction and the rate of the backward
reaction are equal.
57 When a small amount of dilute sulphuric acid When a small amount of dilute sulphuric acid Ais added to an equilibrium system containing is added to the equilibrium system, the
CrO42
(aq) ions and Cr2O72
(aq) ions, the colour concentration of CrO42
(aq) ions decreases while
of the system changes from yellow to orange. that of Cr2O72
(aq) ions increases.
58 When H2(g) and I2(g) are allowed to react in a At equilibrium, both the forward and D
closed container, the rate of the reaction between backward reactions stop.
H2(g) and I2(g) becomes zero when equilibrium
is attained.
59 A reaction with a large Kc can attain equilibrium The value of Kc can be used to predict the D
rapidly. rate at which equilibrium is reached.
60 If Qc is greater than Kc, the system will undergo If Qc is greater than Kc, the system is not C
a net forward reaction until equilibrium is at equilibrium.
reached.
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Unit 40 Factors affectingchemical equilibriumsystems
Fill in the blanks
1 When the concentration of a reactant in an
equilibrium system is increased,
a) a net forward reaction will occur;
b) the position of equilibrium will shift to the
right .
2 When the concentration of a product in an
equilibrium system is increased,
a) a net backward reaction will occur;
b) the position of equilibrium will shift to the
left .
3 An increase in pressure (i.e. a / an decrease
in volume) will bring about a net reaction
that decreases the number of moles of gas,
i.e. the position of equilibrium will shift to the
side of the equation with a fewer number
of moles of gas.
4 A decrease in pressure (i.e. a / an increase
in volume) will bring about a net reaction
that increases the number of moles of gas,
i.e. the position of equilibrium will shift to the
side of the equation with a greater number
of moles of gas.
5 When the temperature of an equilibrium
system with an exothermic forward reaction isincreased,
a) a net backward reaction will occur;
b) the position of equilibrium will shift to
the left ;
c) the value of equilibrium constant, Kc,
will decrease .
6 When the temperature of an equilibrium
system with an endothermic forward reaction is
increased,
a) a net forward reaction will occur;
b) the position of equilibrium will shift to
the right ;
c) the value of equilibrium constant, Kc,
will increase .
True or False
Decide whether each of the following statements is
true or false.
7 If the position of equilibrium lies close Fto the product side, the value of Kc is
small.
8 When the concentration of a reactant in T
an equilibrium system is increased, a net
forward reaction will occur.
9 At a constant temperature, increasing F
the concentration of a reactant in an
equilibrium system will cause Kc to increase.
10 Removing some CaCO3(s) from an F
equilibrium system of CaCO3(s), CaO(s)
and CO2(g) will cause the position of
equilibrium to shift to the CaCO3(s) side.
11 An increase in volume of an equilibrium T
system involving gases will bring about
a net reaction that increases the number
of moles of gas.
12 For an equilibrium system with an Texothermic forward reaction, decreasing
the temperature will shift the position of
equilibrium to the right.
13 Decreasing the temperature will cause F
Kc for an endothermic reaction to
increase.
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14 In the conversion of sulphur dioxide to F
sulphur trioxide in the Contact process,
a pressure of 200 atmospheres is usually
used.
15 The optimum conditions for the Haber F
process are 10 atm and 500 C.
16 A catalyst will not affect the percentage T
of the product in an equilibrium mixture.
Multiple choice questions
17 Consider the following equilibrium system:
N2H4(g) + 2O2(g) 2NO(g) + 2H2O(g)
Which of the following actions can cause the
position of equilibrium to shift to the right?
A Adding N2H4(g)
B Adding H2O(g)
C Removing N2H4(g)
D Removing O2(g) A
18 Consider the following equilibrium system:
CO(g) + H2O(g) CO2(g) + H2(g)
Which of the following actions would cause the
concentration of H2(g) to decrease?A Adding CO(g)
B Adding H2O(g)
C Removing CO2(g)
D Removing H2O(g) D
19 Consider the following equilibrium system:
2KClO3(s) 2KCl(s) + 3O2(g)
Which of the following actions will cause the
position of equilibrium to shift to the left?
A Adding O2(g)
B Adding KCl(s)
C Removing KClO3(s)
D Removing KCl(s) A
20 Consider the following equilibrium system:
N2(g) + 3H2(g) 2NH3(g)
Some NH3(g) is added to the system. Which of
the following combinations is correct?
Net change of [H2(g)] Value of Kc
A Decreases increasesB Decreases remains constant
C Increases increases
D Increases remains constant D
21 Consider the following equilibrium system:
Ca(OH)2(s) Ca2+
(aq) + 2OH(aq)
Adding which of the following substances will
cause the equilibrium concentration of Ca2+
(aq)
ions to increase?
A H2O(l)
B HCl(aq)
C KOH(s)
D Ca(OH)2(s) B
22 Consider the following system at equilibrium:
H2O(g) + CO(g) CO2(g) + H2(g)
The position of equilibrium shifts to the right as
the result of the addition of some extra H2O(g).
How will this shift affect the concentrations of
the other gases?
[CO(g)] [CO2(g)] [H2(g)]
A Increases decreases decreases
B Increases increases decreases
C Decreases decreases increases
D Decreases increases increases D
23 Consider the following equilibrium system:
2CrO42
(aq) + 2H+(aq) Cr2O7
2(aq) + H2O(l)
A solution of Ba(NO3)2 is added, and a BaCrO4precipitate forms. Which of the following
combinations is correct?
Shift of
position of equilibrium Value of Kc
A To the left remains constant
B To the left increases
C To the right remains constant
D To the right decreases A
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24 Consider the following equilibrium system:
H2(g) + I2(g) 2HI(g)
Which of the following graphs represents what
happens when some HI(g) is removed and a new
state of equilibrium is established?
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A
5JNF
B
5JNF
C
5JNF
D
B
25 Consider the following equilibrium system:
C2H6(g) C2H4(g) + H2(g)
Some H2(g) is injected into the system. Which of
the combinations is correct?
Shift of position Change of [H2(g)] relative
of equilibrium to previous equilibrium
A To the left increasesB To the left decreases
C To the right increases
D To the right decreases A
26 Consider the following equilibrium system:
CO2(g) + H2(g) CO(g) + H2O(g)
Which of the following, when added to the system
above, would result in a decrease in [H2O(g)]
relative to the previous equilibrium?
A CO(g)
B CO2(g)
C H2(g)
D H2O(g) A
27 The following equilibrium exists in aqueous
bromine.
Br2(aq) + H2O(l) Br(aq) + 2H
+(aq) + OBr
(aq)
yellow-brown colourless colourless
The yellow-brown colour of aqueous bromine
would fade on adding a few drops of a
concentrated solution of
A HCl.
B KBr.
C AgNO3.
D NaOBr. C
28 Consider the following equilibrium system:
H2(g) + I2(g) 2HI(g)
How will the rates of the forward and backward
reactions change when the volume of the reactionvessel is increased?
Rate of Rate of
forward reaction backward reaction
A Increases increases
B Increases decreases
C Decreases increases
D Decreases decreases D
29 Consider the following equilibrium system:
2NO(g) + O2(g) 2NO2(g)
An equilibrium mixture of NO(g), O2(g) and NO2(g)
is transferred from a 1 dm3
container to a 2 dm3
container.
Which of the following combinations describes
what happens as the system proceeds towards
a new state of equilibrium?
Shift of position Number of
of equilibrium moles of NO2(g)
A To the right increasesB To the right decreases
C To the left increases
D To the left decreases D
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Directions: Questions 30 and 31 refer to the following
information.
At room temperature, N2O4(g) and NO2(g) exist in
equilibrium as follows:
N2O4(g) 2NO2(g)
pale yellow dark brown
A gas syringe is filled with a pale brown mixture of
N2O4(g) and NO2(g) at equilibrium.
/0H
/0H
QMVOHFS
HBTTZSJOHF
SVCCFSDBQ
30 What would be observed when the plunger is
quickly pushed in at time t?
A The mixture first lightens, and then becomes
colourless.
B The mixture first darkens, and then becomes
colourless.
C The mixture first darkens, and then lightens.
D The mixture first lightens, and then darkens.
C
31 Which of the following graphs represents how
the concentration of NO2(g) in the mixture varies
until a new state of equilibrium is established?
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A
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B
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C
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D
U
U U
U
C
32 Consider the following equilibrium system:
PCl5(g) PCl3(g) + Cl2(g)
Which of the following combinations describes
the effect of decreasing the pressure by increasing
the volume?
Shift of position Number ofof equilibrium moles of PCl3(g)
A To the right increases
B To the right decreases
C To the left increases
D To the left decreases A
33 Consider the following equilibrium system:
FeO(s) + H2(g) Fe(s) + H2O(g)
Which of the following combinations describes the
effect of decreasing the volume of the system?
Shift of position
of equilibrium Concentration of H2(g)
A To the right increases
B To the right decreases
C No change increases
D No change decreases C
34 Consider the following equilibrium system:
H2(g) + I2(g) 2HI(g) H < 0
colourless purple colourless
Which of the following combinations describes the
effect of increasing the pressure of the system?
Colour intensity
of the mixture Value of Kc
A Decreases decreases
B Decreases unchanged
C Increases unchanged
D Increases decreases C
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35 In which of the following systems will the position
of equilibrium shift to the right when the pressure
is increased at constant temperature?
A CaCO3(s) CaO(s) + CO2(g)
B 2NO2(g) 2NO(g) + O2(g)
C H2(g) + I2(g) 2HI(g)
D PCl3(g) + Cl2(g) PCl5(g) D
36 In which of the following would the position of
the equilibrium NOT be affected by a volume
change at constant temperature?
A 2NF2(g) N2F4(g)
B C2H6(g) C2H4(g) + H2(g)
C 2NOCl(g) 2NO(g) + Cl2(g)
D CO(g) + H2O(g) H2(g) + CO2(g) D
37 The value of equilibrium constant for a gaseous
reaction will change when
A a catalyst is used.
B the temperature changes.
C the concentrations of products change.
D the volume changes. B
38 Consider the following equilibrium system:
N2(g) + 3H2(g) 2NH3(g) H < 0
Which of the following sets of conditions will
favour the formation of the product?A Low pressure and low temperature
B Low pressure and high temperature
C High pressure and high temperature
D High pressure and low temperature D
39 Consider the following equilibrium system:
2SO2(g) + O2(g) 2SO3(g) H = 197 kJ
Which of the following combinations describes
the effect of increasing the temperature of the
system?
Shift of
position of equilibrium Value of Kc
A To the left increases
B To the left decreases
C To the right increases
D To the right decreases B
Directions: Questions 40 and 41 refer to the following
information.
The hydrogen used in the Haber process is made by
the following reaction:
CH4(g) + H2O(g) CO(g) + 3H2(g) H > 0
40 Which of the following combinations describes the
effect of increasing the pressure of the system?
Equilibrium yield of H2(g) Reaction rate
A Decreases decreases
B Decreases increases
C Increases decreases
D Increases increases B
41 Which of the following combinations describes
the effect of increasing the temperature of the
system?
Equilibrium yield of H2(g) Reaction rate
A Decreases decreases
B Decreases increases
C Increases decreases
D Increases increases D
42 Consider the following graph which relates to
this equilibrium system:
Fe3+
(aq) + SCN(aq) [Fe(SCN)]
2+(aq) H < 0
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43 Consider the following equilibrium system:
Co2+
(aq) + 4Cl(aq) CoCl4
2(aq)
pink blue
When the temperature is increased, the solution
turns dark blue. It can be deduced that the
forward reaction is
A exothermic and the value of Kc has
increased.
B exothermic and the value of Kc has
decreased.
C endothermic and the value of Kc has
increased.
D endothermic and the value of Kc has
decreased. C
44 Consider the following system at fixed pressure:
CH4(g) + H2O(g) CO(g) + 3H2(g) H > 0
What is the effect of a small increase in
temperature on the rate of the forward reaction
(Rf), rate of the backward reaction (Rb), and the
equilibrium constant (Kc)?
Rf Rb KcA Lower higher lower
B Higher lower unchanged
C Higher higher higher
D Higher higher lower C
45 Consider the following equilibrium system:
2H2O(g) + 2Cl2(g) 4HCl(g) + O2(g) H > 0
The temperature of the system is lowered and
the amount of Cl2(g) changes by 1 mole. Which
of the following combinations is correct?
Amount Amount Amount
of Cl2(g) of HCl(g) of O2(g)
A Increase by decrease by decrease by
1 mole 0.5 mole 2 moles
B Increase by decrease by decrease by
1 mole 2 moles 0.5 mole
C Decrease by increase by increase by
1 mole 0.5 mole 2 moles
D Decrease by increase by increase by
1 mole 2 moles 0.5 mole
B
46 Consider the following reaction:
2NO2(g) 2NO(g) + O2(g)
The value of the equilibrium constant for the
reaction is 1.45 x 106
at 227 C and 0.938 at
727 C.
Which of the following combinations concerningthe forward reaction is correct?
Product yield as
Sign of H temperature increases
A + increases
B + decreases
C increases
D decreases A
47 Methanol can be produced by the reaction
between carbon monoxide and hydrogen.CO(g) + 2H2(g) CH3OH(g)
Two experiments were conducted.
Experiment 1: Some CO(g) and H2(g) were placed
in a sealed vessel and the reaction allowed to
proceed at constant temperature.
Experiment 2: Experiment 1 was repeated, but
at a different temperature.
The graph below shows the amount of methanol
produced over the course of Experiments 1 and2.
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"NPVOUPG$)0)H
These results show that Experiment 2 was
conducted at a
A lower temperature than Experiment 1 and the
forward reaction is endothermic.
B lower temperature than Experiment 1 and the
forward reaction is exothermic.
C higher temperature than Experiment 1 and
the forward reaction is endothermic.
D higher temperature than Experiment 1 and
the forward reaction is exothermic. D
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48 Consider the following graph which relates to
this equilibrium system:
N2(g) + 3H2(g) 2NH3(g) H < 0
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Which of the following actions will cause the
concentration changes at time t?
A Addition of N2(g)
B Removal of H2(g)C Decrease in temperature
D Decrease in volume A
Directions: Questions 49 and 50 refer to the following
information.
Consider the following equilibrium system:
CO(g) + 2H2(g) CH3OH(g) H = 91 kJ
49 Which of the following actions will each cause the
position of equilibrium to shift to the right?
A Increase temperature, increase volume
B Increase temperature, decrease volume
C Decrease temperature, decrease volume
D Decrease temperature, increase volume C
50 Which of the following graphs represents the rate
of the forward reaction when the temperature of
the system is increased at time t?
U
U
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A
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B
3BUF
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C
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D
U
U
B
51 In which of the following systems will the position
of equilibrium shift to the left upon an increase
in pressure, but to the right upon an increase in
temperature?
A CO2(g) + H2(g) CO(g) + H2O(g)
H > 0
B C2H6(g) C2H4(g) + H2(g) H > 0C C2H4(g) + H2O(g) C2H5OH(g) H < 0
D 2SO2(g) + O2(g) 2SO3(g) H < 0
B
52 Phosgene (COCl2(g)) is manufactured by passing
carbon monoxide and chlorine through a bed of
carbon which acts as a catalyst.
CO(g) + Cl2(g) COCl2(g) H < 0
Which of the following sets of conditions will
favour the formation of phosgene?A Low pressure and low temperature
B Low pressure and high temperature
C High pressure and low temperature
D High pressure and high temperature C
53 Consider the following equilibrium system:
N2(g) + 3H2(g) 2NH3(g) H < 0
Which of the following graphs shows the effect
of temperature and pressure on the percentage
of NH3(g) in the equilibrium mixture?
P
G/)H
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A B
C D
P
G/)H
5FNQFSBUVSF$
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P
G/)H
5FNQFSBUVSF$
BUN
BUNBUNBUN
P
G/)H
5FNQFSBUVSF$
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D
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54 Consider the following equilibrium system:
PCl3(g) + Cl2(g) PCl5(g) H < 0
Which of the following graphs shows the
relationship between concentration and time as
a result of adding a catalyst at time t?
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U
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1$MH
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A
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C
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D
U
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C
Directions: Questions 55 and 56 refer to the following
information.
Consider the following reaction:
2SO2(g) + O2(g) 2SO3(g) H < 0
55 How can the number of moles of O2(g) at
equilibrium in the system be increased?
A Adding a catalyst
B Decreasing the temperature
C Decreasing the volume of the system
D Adding SO3(g) to the system D
56 Which of the following graphs shows the rate of
the backward reaction when a catalyst is added
to the equilibrium system at time t?
U
U
3BUF
5JNF
A
3BUF
5JNF
B
3BUF
5JNF
C
3BUF
5JNF
D
U
U
B
57 Consider the following equilibrium system:
PCl3(g) + Cl2(g) PCl5(g) H < 0
Which of the following will NOT cause the position
of equilibrium to shift to the right?
A Adding more Cl2(g)
B Adding a catalystC Increasing the pressure
D Decreasing the temperature B
58 Consider the following equilibrium system:
Ag+(aq) + Cl
(aq) AgCl(s)
Which of the following actions will increase the
amount of solid silver chloride of the equilibrium
system?
(1) Adding NaCl(aq)
(2) Adding AgNO3(aq)(3) Removing Cl
(aq)
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3) A
59 Consider the following equilibrium system:
N2H4(g) + 2O2(g) 2NO(g) + 2H2O(g)
Some O2(g) is added to the equilibrium system
and a new state of equilibrium is established.
Which of the following substances have a net
increase in concentration, relative to the previous
equilibrium concentrations?
(1) N2H4(g)
(2) O2(g)
(3) NO(g)
(4) H2O(g)
A (1) and (3) only
B (2) and (4) only
C (1), (2) and (3) only
D (2), (3) and (4) only D
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18
60 The dissociation of a weak acid in aqueous solution
is represented by the following equation:
HA(aq) H+(aq) + A
(aq)
When the above system is at equilibrium, which
of the following statements are correct?
(1) Both HA(aq) and H
+
(aq) are present in thesystem.
(2) More HA(aq) dissociates upon the addition
of NaOH(aq).
(3) Decreasing the pressure shifts the position
of equilibrium to the right.
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3) A
61 For which of the following equilibrium systemswill a decrease in volume at constant temperature
cause a decrease in the amounts of products?
(1) CaCO3(s) CaO(s) + CO2(g)
(2) CH4(g) + H2O(g) CO(g) + 3H2(g)
(3) HCl(g) + H2O(l) H3O+(aq) + Cl
(aq)
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3) A
62 The following reaction reaches equilibrium in a
closed reaction vessel.
C2H4(g) + H2O(g) C2H5OH(g) H < 0
Which of the following action(s) will increase the
mass of C2H5OH(g) in the equilibrium mixture?
(1) Adding a catalyst
(2) Decreasing the volume of the reaction
vessel
(3) Increasing the temperature
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only B
63 Consider the following equilibrium system:
NH4Cl(s) NH3(g) + HCl(g) H > 0
Which of the following actions would favour the
formation of NH3(g)?
(1) Adding a small amount of NH4Cl(s)
(2) Increasing the temperature(3) Increasing the pressure
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only B
64 Consider the following graph which relates to
this equilibrium system:
N2O4(g) 2NO2(g) H > 0
5JNF
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/0H
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Which of the following would cause the
concentration changes at time t?
(1) A change in temperature
(2) A change in pressure
(3) A change in the concentration of NO2(g)
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only A
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65 Hydrogen iodide is formed when hydrogen
and iodine react according to the following
equation.
H2(g) + I2(g) 2HI(g) H = 10 kJ
Which of the following statements about the
equilibrium system is / are correct?
(1) The use of a catalyst would have no effect
on the yield of HI(g).
(2) Increasing the total pressure increases the
yield of HI(g).
(3) Increasing the temperature increases the
yield of HI(g).
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only A
66 Which of the following statements concerning a
catalyst is / are correct?
(1) It decreases the enthalpy change of the
reaction.
(2) It increases the rate of formation of the
products.
(3) It increases the concentration of theproducts.
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only B
Directions : Each question (Questions 67 74) consists of two separate statements. Decide whether each
of the two statements is true or false; if both are true, then decide whether or not the second
statement is a correct explanation of the first statement. Then select one option from A to D
according to the following table :
A Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
B Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.C The 1st statement is false but the 2nd statement is true.
D Both statements are false.
1st statement 2nd statement
67 At a constant temperature, increasing the Increasing the concentration of a reactant C
concentration of a reactant in an equilibrium will cause the position of equilibrium to shift
system will cause Kc to increase. to the product side.
68 Adding some H2(g) to an equilibrium system of When some H2(g) is added to the equilibrium AH2(g), I2(g) and HI(g) will cause a net decrease system, a net reaction will occur to consume
in the concentration of I2(g). some of the H2(g).
69 When the pressure of an equilibrium system When the pressure of an equilibrium system C
involving gases is increased, the position of involving gases is increased, the rate of the
equilibrium must shift to the right. forward reaction will increase.
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20
70 At a constant temperature, changing the The value of Kc for a reversible reaction C
pressure of an equilibrium system of N2(g), H2(g) depends only on temperature.
and NH3(g) has no effect on the position of
equilibrium.
71 Decreasing the pressure of an equilibrium system Decreasing the pressure will bring about a A
of N2O4(g) and NO2(g) will cause more NO2(g) net reaction that increases the number of
to form. moles of gas.
72 Increasing the volume of the reaction vessel of Increasing the volume of the reaction vessel D
an equilibrium system of H2(g), I2(g) and HI(g) of the equilibrium system of H2(g), I2(g) and
will cause the rate of the reaction between HI(g) will cause the position of equilibrium to
H2(g) and I2(g) to increase. shift to the right.
73 When the temperature of an equilibrium system For an equilibrium system with an exothermic D
with an exothermic forward reaction is increased forward reaction, increasing the temperature
by 10 C, the equilibrium constant Kc doubles. will shift the position of equilibrium to the
right.
74 Using iron as a catalyst in the Haber process can A catalyst can increase the rate of the reaction C
increase the yield of ammonia. between nitrogen and hydrogen.
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Part B Topic-based exercise
Multiple choice questions
1 Phosphorus reacts with chlorine according to the
following equation:
P4(s) + 6Cl2(g) 4PCl3(g)
What is the equilibrium constant, Kc, for the
reaction?
A4[PCl3(g)]
[P4(s)]6[Cl2(g)]
B4[PCl3(g)]
6[Cl2(g)]
C[PCl3(g)]
4
[P4(s)][Cl2(g)]6
D[PCl3(g)]
4
[Cl2(g)]6
D
2 Nitrogen dioxide decomposes on heating according
to the following equation:
2NO2(g) 2NO(g) + O2(g)
When 6.80 moles of NO2(g) were put into a
1.00 dm3
container and heated, the equilibrium
mixture contained 1.20 moles of O2(g).
What is the equilibrium constant, Kc, for thereaction?
A 0.357 mol dm3
B 0.655 mol dm3
C 1.53 mol dm3
D 2.80 mol dm3
A
3 Which of the following statements is INCORRECT
for a system at equilibrium?
A The system has a constant mass.
B The system acts so as to opposedisturbances.
C The forward and backward reactions proceed
at the same rate.
D The reactant and product concentrations vary
with time.
D
Directions: Questions 4 and 5 refer to the following
information.
Consider the following reaction:
CO2(g) + H2(g) CO(g) + H2O(g)
1.00 mole of CO2(g) and 2.00 moles of H2(g) are
placed in a 2.00 dm3
container. At equilibrium, the
concentration of CO(g) is 0.280 mol dm3
.
4 What is the equilibrium concentration of
CO2(g)?
A 0.220 mol dm3
B 0.360 mol dm3
C 0.440 mol dm3
D 0.720 mol dm3
A
5 What is the equilibrium constant, Kc, for the
reaction?
A 0.00810
B 0.495
C 2.02
D 123 B
Directions: Questions 6 and 7 refer to the following
information.
In a reversible reaction, propanoic acid and ethanol
react producing an ester and water.
propanoic acid + ethanol ester + water
In an experiment, 1.00 mole of propanoic acid, 1.00
mole of ethanol and 2.00 moles of water were mixed.
At equilibrium, 2.40 moles of water were found to
be present.
6 The equilibrium constant, Kc, for the reaction in
this experiment has the value
A 2.67.
B 1.56.
C 0.643.
D 0.375. A
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7 Which of the following graphs best represents
how the rates of the forward and backward
reactions change over time?
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A
3BUF
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B
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C
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D
C
8 Equal volumes of 1.00 mol dm3
solutions of
W and X are mixed. The reaction below rapidly
reaches equilibrium.
W(aq) + X(aq) Y(aq) + Z(aq)
At equilibrium, the concentration of Y(g) is found
to be 0.400 mol dm3. What is the value of Kc
for the above reaction?
A 0.250
B 0.440
C 4.00
D 16.0 D
9 Consider the following reaction:
N2(g) + 2O2(g) 2NO2(g)
Equal number of moles of N2(g) and O2(g) areplaced, under certain conditions, in a closed
container. Which of the following describes the
changes which occur as the system proceeds
towards equilibrium?
Rate of Concentration
backward reaction of NO2(g)
A Increases increases
B Decreases increases
C Increases decreases
D Decreases decreases A
10 Consider the following equilibrium system:
2O3(g) 3O2(g) Kc = 36.0 mol dm3
What is the concentration of O3(g) when the
equilibrium concentration of O2(g) is 5.80 x 102
mol dm3
?
A 2.32 x 103
mol dm3
B 4.54 x 103
mol dm3
C 3.87 x 102
mol dm3
D 8.70 x 102
mol dm3
A
11 An equal number of moles of steam and chlorine
are placed in a closed container at 375 K. The
following reaction occurs.
2H2O(g) + 2Cl2(g) 4HCl(g) + O2(g)
Kc = 5 x 104
mol dm3
at 375 K
Which of the following relates [Cl2(g)] and
[HCl(aq)] at equilibrium?
A [Cl2(g)] < 2[HCl(g)]
B 2[Cl2(g)] > [HCl(g)]
C [Cl2(g)] = 2[HCl(g)]
D 2[Cl2(g)] = [HCl(g)] B
12 Propanoic acid and ethanol react producing an
ester and water.
propanoic acid + ethanol ester + water
At a certain temperature, the equilibrium constant,
Kc, for the reaction is 2.45.
In an experiment, 2.00 moles of propanoic acid,
2.00 moles of ethanol and 2.40 moles of waterare mixed. What is the equilibrium concentration
of the ester?
A 0.900 mol dm3
B 1.10 mol dm3
C 1.47 mol dm3
D 3.30 mol dm3
A
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13 2SO2(g) + O2(g) 2SO3(g)
Kc = 4.50 dm3
mol1
In an experiment, a mixture of 4.00 moles of
sulphur dioxide and 1.50 moles of oxygen is
allowed to reach equilibrium.
The amount of sulphur trioxide present at
equilibrium would be
A 5.50 moles.
B 4.00 moles.
C 3.00 moles.
D less than 3 moles. D
14 Given the following equilibrium constants:
H2S(aq) H+(aq) + HS
(aq)
Kc = 9.50 x 108
mol dm3
HS
(aq) H+
(aq) + S2
(aq) Kc = 1.00 x 10
19mol dm
3
What is the equilibrium constant for the following
reaction?
S2
(aq) + 2H+(aq) H2S(aq)
A 9.50 x 1027
B 9.75 x 1014
C 9.50 x 1011
D 1.05 x 1026
D
15 Consider the following reaction:
N2(g) + 3H2(g) 2NH3(g)
Kc = 64.0 dm6
mol2
A 1.00 dm3
container is filled with 0.280 mole
of N2(g), 0.600 mole of H2(g) and 0.540 mole
of NH3(g). The system is allowed to reach
equilibrium.
Which of the following combinations is correct
as the system proceeds towards equilibrium?
Directionof net reaction Pressure of system
A Forward increases
B Forward decreases
C Backward increases
D Backward decreases B
16 Consider the following equilibrium:
2NOCl(g) 2NO(g) + Cl2(g)
A flask is filled with NOCl(g), NO(g) and Cl2(g).
Initially there is a total of 5.00 moles of gases
present. When equilibrium is reached, there is a
total of 6.00 moles of gases present. Which of
the following explains this observation?
A A net forward reaction occurs because Qc
Kc.
C A net backward reaction occurs because Qc
< Kc.
D A net backward reaction occurs because Qc
> Kc. A
17 Consider the following equilibrium system:Fe2O3(s) + 3CO(g) 2Fe(l) + 3CO2(g)
Which of the following actions will cause the
position of equilibrium to shift to the right?
A Adding Fe2O3(s)
B Adding Fe(l)
C Removing CO(g)
D Removing CO2(g) D
Directions: Questions 18 and 19 refer to the following
information.
CaCO3(s) CaO(s) + CO2(g)
Kc = 0.100 mol dm3
18 Which of the following changes will cause the
position of equilibrium to shift to the left?
A Adding more CaO(s)
B Removing CaCO3(s)
C Decreasing the volume
D Increasing the surface area of CaO(s) C
19 Initially, 30.0 g of CaCO3(s) were placed in a 2.00
dm3
container. What mass of CO2(g) would be
present at equilibrium?
(Relative atomic masses: C = 12.0, O = 16.0)
A 0.100 g
B 2.20 g
C 8.80 g
D 15.0 g C
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24
Directions: Questions 20 and 21 refer to the following
information.
Consider the following equilibrium system:
2CrO42
(aq) + 2H+(aq) Cr2O7
2(aq) + H2O(l)
A little dilute sulphuric acid is added to the above
equilibrium system.
20 What would be observed?
A The mixture first becomes orange in colour,
and then colourless.
B The mixture first becomes yellow in colour,
and then colourless.
C The mixture becomes orange in colour.
D The mixture becomes yellow in colour. C
21 Which of the following graphs represents how
the concentration of CrO42(aq) ions in themixture varies until a new state of equilibrium is
established?
U
U
5JNF
A
5JNF
B
5JNF
C
5JNF
D
U
U
B
Directions: Questions 22 and 23 refer to the following
information.
The following equilibrium exists in aqueous bromine.
Br2(aq) + H2O(l) Br(aq) + 2H+(aq) + OBr(aq)
A little dilute sodium hydroxide solution is added to
the above equilibrium system.
22 What would be observed?
A The mixture first darkens, and then lightens.
B The mixture first lightens, and then darkens.
C The mixture gets lighter.
D The mixture get darker. C
23 Which of the following graphs represents how theconcentration of Br
(aq) ions in the mixture varies
until a new state of equilibrium is established?
U
U
5JNF
A
5JNF
B
5JNF
C
5JNF
D
U
U
C
24 Tooth enamel, Ca5(PO 4)3OH, establishes the
following equilibrium:
Ca5(PO4)3OH(s)
5Ca2+
(aq) + 3PO43
(aq) + OH(aq)
Which of the following, when added to the
above equilibrium system, will cause the position
of equilibrium to shift to the right?
A H+(aq)
B OH(aq)
C Ca2+
(aq)
D Ca5(PO4)3OH(s) A
25 Each of the following equilibrium systems is
disturbed by increasing the pressure as a result
of decreasing the volume.
In which of the systems will the number of moles
of products increase?
A 2CO2(g) 2CO(g) + O2(g)
B N2F4(g) 2NF2(g)
C Si(s) + 2Cl2(g) SiCl4(g)
D N2(g) + C2H2(g) 2HCN(g) C
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Directions: Questions 26 and 27 refer to the following
information.
The diagram below shows a gas syringe containing
a pale brown mixture of N2O4(g) and NO2(g) at
equilibrium at room temperature:
N2O4(g) 2NO2(g)
pale yellow dark brown
/0H
/0H
QMVOHFS
HBTTZSJOHF
SVCCFSDBQ
Some N2O4(g) is added to the gas syringe at time t
while the volume and the temperature of the mixture
are both kept constant.
26 What would be observed?
A The mixture first darkens, and then lightens.
B The mixture first lightens, and then becomes
colourless.
C The mixture gradually gets darker.
D The mixture gradually becomes colourless.
C
27 Which of the following graphs represents how
the concentration of NO2(g) in the mixture varies
until a new state of equilibrium is established?
U
U
5JNF
A
5JNF
B
5JNF
C
5JNF
D
U
U
C
28 The system below reaches equilibrium in a closed
reaction vessel.
4HCl(aq) + MnO2(s)
Cl2(g) + 2H2O(l) + Mn2+
(aq) + 2Cl(aq)
H < 0
Which of the following actions will increase the
mass of Cl2(g) in the equilibrium mixture?
A Adding some MnO2(s)
B Increasing the temperature
C Decreasing the volume of the reaction vessel
D Adding something that precipitates the
Mn2+
(aq) ions D
29 Consider the following graph which relates to
this equilibrium system:
CH3COOH(aq) + H2O(l)
CH3COO(aq) + H3O+(aq) H < 0
5JNFU
Which of the following actions caused the change
in the concentration of H3O+(aq) at time t?
A Addition of HCl(aq)
B Decreasing the temperature
C Addition of CH3COO(aq) ions
D Increasing the volume of the container C
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26
Directions: Questions 30 and 31 refer to the following
information.
The hydrogen used in the Haber process is made by
the following reaction:
CH4(g) + H2O(g) CO(g) + 3H2(g)
HO
= +206 kJ
30 Which of the following sets of conditions will
favour the formation of hydrogen?
A Low pressure and low temperature
B Low pressure and high temperature
C High pressure and low temperature
D High pressure and high temperature B
31 Equal amounts of CH4(g) and H2O(g) are placed in
a reaction vessel and allowed to react. After 10
minutes, equilibrium has been reached. At thattime, some H2(g) is added to the mixture and a
new state of equilibrium is established.
Which of the following graphs represents the
changes in the concentrations of CH4(g) and H2(g)
in the reaction mixture?
$POD
FOUSBUJPO
NP
MENm
$POD
FOUSBUJPO
NP
MENm
$PODFOUSBUJPO
NPMENm
$PODFOUSBUJPO
NPMENm
5JNFNJO
5JNFNJO
5JNFNJO 5JNFNJO
A B
C D
B
32 Consider the following equilibrium system in a
closed reaction vessel:
CH3CHO(g) CH4(g) + CO(g) H > 0
What would happen if some CH4(g) is added to
the system?
A The amounts of all substances increase, relativeto their previous equilibrium amounts.
B The value of Kc increases.
C The amounts of CH3CHO(g) and CO(g) both
increase, relative to their previous equilibrium
amounts.
D The amounts of CH3CHO(g) and CH4(g) both
increase, relative to their previous equilibrium
amounts. D
33 The graph below shows the effect of temperature
and pressure on the equilibrium yield of theproduct in a gaseous equilibrium system.
5FNQFSBUVSF
BUN
BUN
BUN
:JFMEPGQSPEVDU
Which of the following reactions would have the
relationship between the yield, temperature and
pressure shown in the graph?
A H2(g) + I2(g) 2HI(g) H > 0
B PCl3(g) + Cl2(g) PCl5(g) H < 0
C N2O4(g) 2NO2(g) H > 0
D CH3CH(OH)CH3(g)
CH3COCH3(g) + H2(g) H < 0 C
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Directions: Questions 34 and 35 refer to the following
information.
Methanol is manufactured by the reaction of carbon
monoxide with hydrogen in the presence of a ZnO /
Cr2O3 catalyst:
ZnO / Cr2O3
CO(g) + 2H2(g) CH3OH(g)
34 Which of the following combinations describes the
effect of increasing the pressure of the system?
Equilibrium yield Reaction rate
A Decreases increases
B Decreases decreases
C Increases increases
D Increases decreases C
35 Which of the following combinations describesthe effect of removing the catalyst from the
system?
Equilibrium yield Reaction rate
A Decreases decreases
B No change decreases
C No change no change
D Decreases no change B
36 Transport of oxygen in the body involves
the complex molecules haemoglobin andoxyhaemoglobin.
haemoglobin + oxygen oxyhaemoglobin
If carbon monoxide (CO) is present in the air,
poisoning can occur because
A the equilibrium constant for the reaction is
reduced.
B CO reacts with oxygen to form CO2, driving
the equilibrium to the left.
C the position of equilibrium shifts to the left
because haemoglobin bonds strongly withCO.
D CO cata lyzes the decomposit ion of
oxyhaemoglobin into haemoglobin and
oxygen. C
Directions: Questions 37 and 38 refer to the following
information.
The equilibrium constant, Kc, for the thermal
decomposition of calcium carbonate is 2.70 x 103
mol dm3
at 1 000 K.
CaCO3(s) CaO(s) + CO2(g) H > 0
15.0 g of CaCO3(s) are introduced into a 5.00 dm3
evacuated vessel, and the system is allowed to attain
equilibrium at 1 000 K.
37 What is the percentage of decomposition of
CaCO3(s) in the equilibrium system?
(Relative atomic masses: C = 12.0, O = 16.0, Ca
= 40.1)
A 1.80%
B 4.05%C 9.00%
D 13.9% C
38 Which of the following actions will cause the
percentage of decomposition of CaCO3(s) of the
equilibrium system to increase?
(1) Adding some CaCO3(s)
(2) Increasing the temperature
(3) Removing some CaO(s)
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only B
39 Consider the following reaction:
2NOCl(g) 2NO(g) + Cl2(g)
Initially, some NOCl(g) is placed in an empty flask.
Which of the following statements describe the
changes which occur as the system proceeds
towards equilibrium?
(1) The rate of the backward reaction
increases.
(2) The concentration of NOCl(g) increases.
(3) The concentration of NO(g) increases.
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3) B
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28
40 Consider the following equilibrium system:
NO2Cl(g) + NO(g) NOCl(g) + NO2(g)
Adding which of the following substances will
cause the equilibrium concentration of NO2(g) to
increase?
(1) NOCl(g)(2) NO(g)
(3) NO2Cl(g)
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only D
41 Consider the following equilibrium system:
2SO2(g) + O2(g) 2SO3(g)
K
c = 1.20 x 10
4
dm
3
mol
1
Some SO2(g) is added to the equilibrium system.
Which of the following statements are correct?
(1) The position of equilibrium shifts to the
right.
(2) The r ate o f th e for ward rea ction
increases.
(3) The value of Kc increases.
A (1) and (2) only
B (1) and (3) only
C (2) and (3) onlyD (1), (2) and (3) A
42 Consider the following equilibrium system:
N2O4(g) 2NO2(g) H = +58 kJ
pale yellow dark brown
Shifting the position of equilibrium to the left is
accompanied by
(1) an increase in the volume of the system.
(2) a release of heat by the system to the
surroundings.
(3) a decrease in the average relative molecular
mass of the gas molecules in the system.
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only B
43 Consider the following equilibrium system:
PCl3(g) + Cl2(g) PCl5(g)
Which of the following statements is / are correct
when the volume of the system is decreased?
(1) The position of equilibrium shifts to the
right.(2) The rate of the backward reaction is greater
than that of the forward reaction.
(3) The value of Kc decreases.
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only A
44 For which of the following equilibrium systems
will the amounts of reactants increase with an
increase in the container volume?
(1) C(g) + CO2(g) 2CO(g)
(2) N2(g) + 3H2(g) 2NH3(g)
(3) 2NO(g) + O2(g) 2NO2(g)
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only D
45 Chlorine trifluoride, a colourless gas, can be
decomposed into its element.
2ClF3(g) 3F2(g) + Cl2(g) HO
= +159 kJ
Which of the following statements is / are
correct?
(1) The decomposition is a redox reaction.
(2) When an equilibrium mixture is heated,
its colour fades.
(3) When the volume of the container of
an equilibrium mixture is increased, more
Cl2(g) will form.
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only C
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46 Consider the following equilibrium system:
2NO(g) + Br2(g) 2NOBr(g) H < 0
Which of the following actions will cause the
position of equilibrium to shift to the right?
(1) Adding some NO(g)
(2) Increasing the volume(3) Decreasing the temperature
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3) B
47 Consider the following equilibrium system in a
closed reaction vessel:
CO(g) + 2H2(g) CH3OH(g) H < 0
Which of the following action(s) can cause anincrease in the value of Kc?
(1) Adding some CO(g)
(2) Decreasing the temperature
(3) Transferring the reaction mixture to a vessel
of larger volume
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only B
48 Consider the following equilibrium system:
Cu2+
(aq) + 4Br(aq) CuBr4
2(aq)
blue colourless green
Cooling the system changes its colour from green
to blue.
Which of the following statements is / are
correct?
(1) The forward reaction is exothermic.
(2) The value ofK
c decreases when the systemis cooled.
(3) A net backward reaction occurs when the
system is cooled.
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only D
49 Consider the following equilibrium system:
CO(g) + H2O(g) CO2(g) + H2(g)
H = 41 kJ mol1
Which of the following will cause a shift in the
position of equilibrium?
(1) Adding a catalyst(2) Changing the temperature
(3) Changing the volume
A (1) only
B (2) only
C (1) and (3) only
D (2) and (3) only B
50 Which of the following statements about enzymes
are correct?
(1) Enzymes are proteins.(2) Enzymes increase the rate of biochemical
reactions.
(3) Enzymes increase the equilibrium constant
of biochemical reactions.
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3) A
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30
Directions : Each question (Questions 51 60) consists of two separate statements. Decide whether each
of the two statements is true or false; if both are true, then decide whether or not the second
statement is a correct explanation of the first statement. Then select one option from A to D
according to the following table :
A Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
B Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.C The 1st statement is false but the 2nd statement is true.
D Both statements are false.
1st statement 2nd statement
51 All chemical equilibrium systems have equal At equilibrium, both the forward and backward D
concentrations of reactants and products. reactions stop.
52 Adding some O2(g) to an equilibrium system of When some O2(g) is added to the equilibrium A
SO2(g), O2(g) and SO3(g) will cause a net increase system, a net reaction will occur to consumein the concentration of SO3(g). some of the O2(g).
53 Adding some CaO(s) to an equilibrium system Adding some CaO(s) to the equilibrium system D
of CaCO3(s), CaO(s) and CO2(g) will cause the will cause the value of Kc to increase.
position of equilibrium to shift to the left.
54 Keeping the volume constant, adding some The new equilibrium concentration of NO2(g) C
NO2(g) to an equilibrium system of N2O4(g) and will increase relative to its previous equilibrium
NO2(g) will cause the mixture to get darker concentration.
gradually.
55 Decreasing the volume of the container of an Decreasing the volume of the container of A
equilibrium system of H2(g), I2(g) and HI(g) will the equilibrium system will cause the
cause the purple colour of the system to become concentration of I2(g) to increase.
deeper.
56 When the volume of the gas syringe containing Increasing the volume of the gas syringe C
an equilibrium system of N2O4(g) and NO2(g) is containing the equilibrium system will cause
increased, the mixture first darkens and then more NO2(g) to form.
lightens.
57 For an equilibrium system with an endothermic For an equilibrium system with an endothermic Cforward reaction, increasing the temperature forward reaction, increasing the temperature
will cause the position of equilibrium to shift will cause the value Kc to increase.
to the left.
58 A temperature of 1 000 C is usually used in Increasing the temperature will increase the D
the Haber process. yield of ammonia in the Haber process.
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59 The pressure used for converting sulphur dioxide Increasing the pressure will increase the yield C
to sulphur trioxide in the Contact process is of sulphur trioxide.
usually 200 atmospheres.
60 Catalysts are used in many industrial processes. Catalysts will not affect the percentage of the B
product in the equilibrium mixture.
Short questions
61 For each of the following equilibrium system,
(i) write an expression for the equilibrium constant, Kc;
(ii) State the units of Kc.
a) Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g) (2 marks)
Kc =
[CO2(g)]3
[CO(g)]3 (1)
Kc has no units. (1)
b) MgCO3(s) MgO(s) + CO2(g) (2 marks)
Kc = [CO2(g)] (1)
The units of Kc are mol dm3
. (1)
c) 3O2(g) 2O3(g) (2 marks)
Kc =
[O3(g)]2
[O2(g)]3 (1)
The units of Kc are dm3
mol1
. (1)
d) CO(g) + 2H2(g) CH3OH(g) (2 marks)
Kc =
[CH3OH(g)]
[CO(g)][H2(g)]2 (1)
The units of Kc are dm6
mol2
. (1)
62 Given the following reactions and their corresponding equilibrium constants at 1 292 C:
2H2O(g) 2H2(g) + O2(g) Kc1 = 1.60 x 1011
mol dm3
2CO2(g) 2CO(g) + O2(g) Kc2 = 1.30 x 1010
mol dm3
Calculate the equilibrium constant, Kc3, for the following reaction
CO2(g) + H2(g) H2O(g) + CO(g)
at the same temperature. (3 marks)
Kc1 =
[H2(g)]2[O2(g)]
[H2O(g)]2
Kc2 =[CO(g)]
2[O2(g)]
[CO2(g)]2
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32
Kc3 =
[H2O(g)][CO(g)]
[CO2(g)][H2(g)] (1)
=
1
Kc1x Kc2
=
1
1.60 x 1011
mol dm3
x 1.30 x 1010
mol dm3
(1)
= 2.85 (1)
63 When bromine is dissolved in water, the following equilibrium system is established:
Br2(l) + H2O(l) H+(aq) + Br
(aq) + HOBr(aq)
yellow-brown
colourless
In an experiment, dilute sodium hydroxide solution and then dilute hydrochloric acid are added to the system.
The observations made are listed below.
Step Procedure Observation
I Adding dilute sodium hydroxide solution A colourless solution is formed
II Adding dilute hydrochloric acid to the resulting solution A yellow-brown solution is formed
Explain the observations using Le Chateliers principle. (6 marks)
When dilute sodium hydroxide solution is added, the hydroxide ions react with the hydrogen ions to form water. Thus, the
concentration of hydrogen ions decreases. (1)
The system responds by reducing this change. (1)
A net forward reaction occurs to produce more hydrogen ions. (1)
A colourless solution is observed as the concentration of Br2(aq) decreases. (1)
When hydrogen ions are added, the system responds by reducing this change.
A net backward reaction occurs to consume some of the hydrogen ions. (1)
A yellow-brown solution is observed as the concentration of Br2(aq) increases. (1)
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64 Each of the following equilibrium systems is disturbed by increasing the pressure as a result of decreasing
the volume of the reaction vessel. Decide whether the number of moles of reaction product(s) will increase,
decrease, or remain the same. Explain your answer in each case.
a) 2CO2(g) 2CO(g) + O2(g) (3 marks)
An increase in pressure will bring about a net reaction that decreases the number of moles of gas. This helps to reduce
the pressure. (1)
A net backward reaction occurs. (1)
Thus, the number of moles of reaction products will decrease. (1)
b) CO(g) + H2O(g) CO2(g) + H2(g) (3 marks)
The number of moles of gas is the same on both sides of the equation, (1)
so changing the pressure has no effect on the position of equilibrium. (1)
Thus, the number of moles of reaction products will remain the same. (1)
c) Si(s) + 2Cl2(g) SiCl4(g) (3 marks)
An increase in pressure will bring about a net reaction that decrease the number of moles of gas. This helps to reduce
the pressure. (1)
A net forward reaction occurs. (1)
Thus, the number of moles of reaction product will increase. (1)
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34
65 Consider the reaction between copper(II) ions and chloride ions:
Cu2+
(aq) + 4Cl(aq) CuCl4
2(aq)
blue yellow
The Cu2+
(aq) ion is blue while the CuCl42
(aq) ion is yellow, so a mixture of these two appears green.
The table below lists the colour of two samples of equilibrium mixture of the same composition kept at
different temperatures.
Temperature Colour of equilibrium mixture
10 C blue
90 C green
Deduce and explain whether the forward reaction is exothermic or endothermic. (3 marks)
When the system is cooled, it appears blue because the concentration of Cu2+
(aq) ions increases. (1)
It can be deduced that when the temperature is decreased, the system will undergo a net backward reaction so as to raise
the temperature. (1)
Thus, the backward reaction should be an exothermic reaction. / The forward reaction should be an endothermic reaction. (1)
66 Consider the following equilibrium system in a closed container:
CaCO3(s) CaO(s) + CO2(g) H > 0
Complete the table to describe the effect of various actions on the position of equilibrium of the system.
(5 marks)
Action Position of equilibrium
(a) The volume of the reaction vessel is increased. shifts to the right (1)
(b) Some CaCO3(s) is removed. no effect (1)
(c) Some CO2(g) is added. shifts to the left (1)
(d) A few drops of NaOH(aq) are added. shifts to the right (1)
(e) The temperature is increased. shifts to the right (1)
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67 In the manufacture of nitric acid, ammonia is oxidized to nitrogen monoxide by the following reaction:
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) HO
= 906 kJ
In an experiment, a mixture of NH3(g), O2(g), NO(g) and H2O(g) is allowed to reach equilibrium in a cylinder
fitted with a movable piston. Give the effect of each of the following changes on items listed in the table
below:
a) Adding a catalyst (2 marks)
b) Increasing the temperature (2 marks)
c) Increasing the pressure by decreasing the volume (2 marks)
Effect of change on (a) Adding a catalyst(b) Increasing the
temperature(c) Increasing the pressure
the rate of the
forward reactionincreases (0.5) increases (0.5) increases (0.5)
the rate of the
backward reactionincreases (0.5) increases (0.5) increases (0.5)
the position of
equilibriumno effect (0.5) shifts to the left (0.5) shifts to the left (0.5)
the equilibrium
constant, Kcno effect (0.5) decreases (0.5) no effect (0.5)
68 A particular industrial process involves the following steps.
B(g) and C(g) recycling
Reaction 1
A(g) + B(g) 2C(g)
H= +100 kJ
Reaction 2
2C(g) + B(g) 2D(g)
H= 150 kJ
temperature 300 C
pressure 10 atm
A(g) B(g)
B(g)
separation chamber product D(g)
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a) It is possible to alter the temperature and pressure at which Reaction 2 occurs.
In the table below, indicate what effect the following changes would have on the rate, equilibrium yield
and value of the equilibrium constant, Kc, for Reaction 2. (3 marks)
Would the rate of
Reaction 2 become
higher, lower or remain
unchanged?
Would the equilibrium
yield of Reaction 2
become higher, lower or
remain unchanged?
Would the value of Kc
of Reaction 2 become
higher, lower or remain
unchanged?
The temperature of
Reaction 2 is increased to
600 C.
higher (0.5) lower (0.5) lower (0.5)
The pressure of Reaction
2 is decreased to 5 atm
at constant temperature.
lower (0.5) lower (0.5)remain
unchanged (0.5)
b) Heat is released in Reaction 2. Describe how the heat can be used within this industrial process.
(1 mark)
Provide heat for Reaction 1. / Increase the rate of Reaction 1. / Heat the incoming reactants. / Generate electricity. (1)
Structured questions
69 When nitrogen monoxide reacts with oxygen, a dynamic equilibrium is established.
2NO(g) + O2(g) 2NO2(g) HO
= 115 kJ
a) State TWO features of a system that is in dynamic equilibrium. (2 marks)
Rate of forward reaction = rate of backward reaction. (1)
Concentrations of the reactants and products remain constant. (1)
b) At a certain temperature, the equilibrium constant, Kc, for the reaction is 65.0 dm3
mol1
.
The concentrations of NO(g) and O2(g) in an equilibrium mixture are 0.600 mol dm3
and 0.300 mol dm3
respectively. What is the equilibrium concentration of NO2(g)? (2 marks)
Kc =[NO2(g)]
2
[NO(g)]2[O2(g)]
65.0 dm3 mol1 = [NO2(g)]2
(0.600 mol dm3
)2(0.300 mol dm
3)
(1)
[NO2(g)] = 2.65 mol dm3
(1)
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c) In each of the following cases, sketch on the given graph to show the expected variation in the concentration
of NO2(g) in the equilibrium mixture in (b) until the attainment of a new state of equilibrium. Explain your
answer in each case.
i) Some O2(g) is introduced into the equilibrium mixture at time t1, while the volume and the temperature
are both kept constant. (2 marks)
5JNF
U
An increase in the concentration of O2(g) will shift the position of equilibrium to the right. (1)
Thus, the concentration of NO2(g) will increase.
ii) The temperature of the equilibrium mixture is increased at time t2. (3 marks)
5JNF
U
When the temperature is increased, the system will respond by reducing the temperature. (1)
As the backward reaction is endothermic, the system will undergo a net backward reaction. Thus, the concentration
of NO2(g) will decrease. (1)
d) State and explain how the pressure should be changed to give a higher yield of NO2(g). (2 marks)
Increase the pressure. (1)
An increase in pressure will bring about a net reaction that decreases the number of moles of gas. This helps to reduce
the pressure. (1)
A net forward reaction will occur.
Thus, the yield of NO2(g) will increase.
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70 The ester ethyl ethanoate is hydrolyzed when it is heated with water in the presence of an acid catalyst. An
equilibrium is established.
CH3COOCH2CH3(l) + H2O(l) CH3COOH(l) + CH3CH2OH(l)
a) A 0.600 mole sample of ethyl ethanoate was heated with 4.00 mole of water. At equilibrium, 68.0% of
the ester was hydrolyzed. Calculate the equilibrium constant, Kc, for this reaction. (4 marks)
Number of moles of ester reacted = 0.600 mol x 68.0% = 0.408 mol
Number of moles of ester in equilibrium mixture = (0.600 0.408) mol = 0.192 mol (0.5)
Number of moles of water in equilibrium mixture = (4.00 0.408) mol = 3.59 mol (0.5)
Number of moles of ethanoic acid in equilibrium mixture = 0.408 mol (0.5)
Number of moles of ethanol in equilibrium mixture = 0.408 mol (0.5)
Let Vdm3
be the total volume of the equilibrium mixture.
Kc =
[CH3COOH(l)][CH3CH2OH(l)]
[CH3COOCH2CH3(l)][H2O(l)]
=(
0.408
V ) (0.408
V )
(0.192
V ) (3.59
V )(1)
= 0.242 (1)
b) A student repeated the experiment using the same initial quantities. During the experiment she noticedthat the water in the condenser had stopped flowing. There was a sweetish smell coming from the top
of the condenser.
What effect, if any, will this problem have on
i) the concentrations of the products in the flask? (2 marks)
Ester was lost. (1)
The concentrations of the products would decrease. (1)
ii) the value of the equilibrium constant, Kc?
Explain your answer in each case. (2 marks)
The value of Kc would remain constant. (1)
The value of Kc does not change with concentration. / The value of Kc only changes with temperature. (1)
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71 Hydrogen gas can be made from carbon monoxide and steam as shown by the following equation.
CO(g) + H2O(g) CO2(g) + H2(g)
The diagram below shows how the concentrations of H2O(g) and H2(g) change with time as equilibrium is
established.
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)0H
9
$PODFOUSBUJPO
a) On the time axis mark with an X the time at which equilibrium is first established. (1 mark)
b) State Le Chateliers principle. (2 marks)
Le Chateliers principle states that if the condition of a system in equilibrium is changed, the position of equilibrium
will shift (1)
so as to reduce that change. (1)
c) The volume and the temperature of the equilibrium mixture are both kept constant. Predict the effect of
each of the following changes on the position of equilibrium:
i) adding carbon monoxide to the equilibrium mixture; and (2 marks)
The system responds by reducing the change. A net forward reaction occurs to use up some of the extra carbon
monoxide. (1)
The position of equilibrium shifts to the right. (1)
ii) removing steam from the equilibrium mixture. (2 marks)
The system responds by reducing the change. A net backward reaction occurs to produce more steam. (1)
The position of equilibrium shifts to the left. (1)
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d) This reaction is usually carried out at 450 C.
i) State and explain the effect on the rate of production of hydrogen if this reaction is carried out at a
temperature above 450 C. (3 marks)
The rate of production of hydrogen will increase. (1)
The reactant particles have more energy and collide more often. (1)
A larger portion of the reactant particles have energy equal to or greater than the activation energy. (1)
ii) State and explain the effect on the yield of hydrogen if the reaction is carried out in the presence of
a catalyst. (2 marks)
No effect on the yield of hydrogen. (1)
A catalyst increases the rates of both the forward reaction and the backward reaction to the same extent. (1)
72 Methanol can be produced by using a reversible reaction between carbon monoxide and hydrogen.
2H2(g) + CO(g) CH3OH(g)
When 2.00 mole of hydrogen and 1.00 mole of carbon monoxide are mixed and heated to a high temperature
in a container of volume 1.50 dm3, the equilibrium yield of methanol is 0.800 mole.
a) Calculate a value for the equilibrium constant, Kc, for this reaction at this temperature and give its
units. (4 marks)
2H2(g) + CO(g) CH3OH(g)
According to the equation, 2 moles of H2(g) react with 1 mole of CO(g) to give 1 mole of CH 3OH(g).
As 0.800 mole of