chem. equilibrium

7/30/2019 Chem. Equilibrium

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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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2

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?

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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

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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


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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4

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.


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?

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GPSXBSESFBDUJPO

CBDLXBSESFBDUJPO

LFZ

A

3BUF

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B

3BUF

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C

3BUF

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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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9HBOE:H

9:H

/VNCFSPGNPMFT


reaction?

A 0.0278

B 0.167

C 6.00

D 36.0 D


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

.


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


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.


How many moles of gas were present in the

equilibrium mixture?

A 0.50

B 1.00

C 1.50

D 2.00 C


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


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


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


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


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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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


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


(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


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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10

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.



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


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


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


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


D Increases remains constant D


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


2CrO42


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


12/77

12


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

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B

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C

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D

B


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


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


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


B Increases decreases

C Decreases increases

D Decreases decreases D


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


13/77


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.

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/0H

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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

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C




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


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


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


B Decreases unchanged

C Increases unchanged

D Increases decreases C


14/77

14

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


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


2SO2(g) + O2(g) 2SO3(g) H = 197 kJ


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


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


Equilibrium yield of H2(g) Reaction rate




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




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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15/77


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


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


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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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


16/77

16



N2(g) + 3H2(g) 2NH3(g) H < 0

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concentration changes at time t?

A Addition of N2(g)

B Removal of H2(g)C Decrease in temperature

D Decrease in volume A


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


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?

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B

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C

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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


C High pressure and low temperature

D High pressure and high temperature C


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?

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A B

C D

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17/77


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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information.


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

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A

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B

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C

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D

U

U

B


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


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


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


18/77

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


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




N2O4(g) 2NO2(g) H > 0

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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


19/77

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


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










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.


20/77

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.


21/77

Part B Topic-based exercise


1 Phosphorus reacts with chlorine according to the

following equation:

P4(s) + 6Cl2(g) 4PCl3(g)


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


information.


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


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


22/77

22

7 Which of the following graphs best represents

how the rates of the forward and backward

reactions change over time?

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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


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


Rate of Concentration

backward reaction of NO2(g)




D Decreases decreases A


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


23/77

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


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:


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)



A Adding Fe2O3(s)

B Adding Fe(l)

C Removing CO(g)

D Removing CO2(g) D


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


24/77

24


information.

Consider the following equilibrium system:

2CrO42


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


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


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.


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


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


25/77


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)


/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.


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


the concentration of NO2(g) in the mixture varies


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



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


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


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


27/77


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


Equilibrium yield Reaction rate

A Decreases increases

B Decreases decreases


D Increases decreases C

35 Which of the following combinations describesthe effect of removing the catalyst from the

system?

Equilibrium yield Reaction rate


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


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




Initially, some NOCl(g) is placed in an empty flask.

Which of the following statements describe the

changes which occur as the system proceeds


(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


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


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


N2O4(g) 2NO2(g) H = +58 kJ


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



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


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


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


29/77


2NO(g) + Br2(g) 2NOBr(g) H < 0



(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



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



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


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









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


32/77

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)


33/77

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)


34/77

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)


35/77

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)


36/77

36

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)


37/77

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.


38/77

38

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)


39/77

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.

5JNF

)H

)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

chem. equilibrium

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