The Equililbrium Constant, Kp Exam-style MCQs | A-Level Chemistry CIE

Question 1

The equilibrium involving phosphorus(V) chloride, phosphorus(III) chloride and chlorine gas is

PCl_5(g) ⇌ PCl_3(g) + Cl_2(g)

The numerical value of K_p is 1.8 at 250°C.

The expression for the partial pressure of chlorine gas is

A

total pressure × (moles of chlorine gas ÷ total moles of gas)

B

total pressure × moles of chlorine gas

C

total pressure ÷ (moles of chlorine gas ÷ total moles of gas)

D

total pressure ÷ moles of chlorine gas

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Question 2

Sulfur dioxide and oxygen react to form sulfur trioxide. The reaction is reversible.

2SO_2(g) + O_2(g) ⇌ 2SO_3(g) K_p = 2.96 × 10^-9Pa^-1 at 700°C

The reaction is allowed to reach equilibrium at 700°C. The partial pressure of O_2(g) is 375 kPa and the partial pressure of SO_3(g) is 20.3 kPa.

What is the partial pressure of SO_2(g)?

A

19.3 kPa

B

609 kPa

C

18,300 kPa

D

609,000 kPa

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Question 3

In this question you should assume that all gases behave ideally.

Hydrogen and iodine react reversibly in the following reaction. The system reaches dynamic equilibrium.

H_2(g) + I_2(g) ⇌ 2HI_(g) ∆H = -9.5 kJ mol^-1

Which statement must be true for the K_p of this equilibrium to be constant?

A

the partial pressures of H₂, I₂ and HI are equal

B

the external pressure is constant

C

the forward and reverse reactions have stopped

D

the temperature is constant

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Question 4

Hydrogen iodide dissociates into hydrogen and iodine.

2HI_(g) ⇌ H_2(g) + I_2(g)

In an experiment, b mol of hydrogen iodide were put into a sealed vessel at pressure p. At equilibrium, x mol of the hydrogen iodide had dissociated.

Which expression for K_p is correct?

(b−x)2x2

(b−x)2x2p2

4b(b−x)x2p2

4(b−x)2x2

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Question 5

Methanol can be produced from hydrogen and carbon monoxide.

2H_2(g) + CO_(g) ⇌ CH₃OH_(g)

What is the expression for K_p for this reaction?

Kp=p(CH3OH)2p(H2)2×p(CO)

Kp=p(CH3OH)p(H2)2×p(CO)

Kp=p(H2)2×p(CO)p(CH3OH)

Kp=p(CO)×2p(H2)2p(CH3OH)

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Question 6

The equation for the reaction between carbon monoxide and hydrogen is shown.

CO_(g) + 3H_2(g) ⇌ CH_4(g) + H₂O_(g)

What are the units of K_pfor this reaction?

A

kPa

B

kPa^-1

C

kPa²

D

kPa^-2

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Question 7

The reversible reaction of nitrogen and hydrogen to form ammonia is shown below.

N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

In the equilibrium mixture, the partial pressure of N₂is 18.75 MPa and the partial pressure of H₂is 2.50 MPa.

The total pressure is 25 MPa.

What is the value of K_p, in MPa^-2?

A

1.2 × 10^-4

B

0.048

C

0.075

D

21

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Question 8

The reversible reaction of sulfur dioxide and oxygen to form sulfur trioxide is shown below.

2SO_2(g) + O_2(g) ⇌ 2SO_3(g)

An equilibrium mixture contains 2.4 mol SO₂, 1.2 mol O₂and 0.4 mol SO₃.

The total pressure is 250 atm.

What is the partial pressure of SO₃?

A

15 atm

B

25 atm

C

100 atm

D

200 atm

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Question 9

An equilibrium mixture is prepared in a container of fixed volume.

CO_(g) + Cl_2(g) ⇌ COCl_2(g) ΔH = -108 kJ mol^-1

The temperature of this mixture is decreased and the mixture is allowed to reach a new equilibrium.

Which is greater for the new equilibrium than for the original equilibrium?

A

the mole fraction of carbon monoxide

B

the partial pressure of chlorine

C

the total pressure of the mixture

D

the value of the equilibrium constant, K_p

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Question 10

When one mole of ammonia is heated to a given temperature, 50% of the compound dissociates and the following equilibrium is established.

NH_3(g) ⇌ $\frac{1}{2}$ N_2(g) + $\frac{3}{2}$ H_2(g)

What is the total number of moles of gas present in this equilibrium mixture?

A

1.5

B

2.0

C

2.5

D

3.0

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Question 11

The equation for the reaction between sulfur dioxide and oxygen is shown.

2SO_2(g) + O_2(g) ⇌ 2SO_3(g)

In an experiment, 2.00 mol of sulfur dioxide are mixed with 2.00 mol of oxygen.

The total amount of the three gases at equilibrium is 3.40 mol

What is the mole fraction of sulfur trioxide in the equilibrium mixture?

A

0.176

B

0.353

C

0.600

D

1.200

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Question 12

Nitrogen reacts with hydrogen in this exothermic reaction

N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

Which change increases the equilibrium yield of ammonia but has no effect on the value of the equilibrium constant K_p?

A

add a catalyst

B

increase the partial pressure of nitrogen

C

decrease the temperature

D

decrease the total pressure

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