The Equilibrium Constant, Kc Exam-style MCQs | A-Level Chemistry CIE

Question 1

Equal amounts of W and X are mixed and allowed to reach equilibrium.

W + X ⇌ Y + Z

The value of the equilibrium constant is K_c = 4.85. At equilibrium, the mixture will contain

almost all Y and Z

almost all W and X

W, X, Y and Z but there is less Y and Z than W and X

W, X, Y and Z but there is more Y and Z than W and X

Question 2

One mole of phosphorus(V) chloride, PCl₅, is heated to 600 K in a sealed flask of volume 1 dm³.

Equilibrium is established and measurements are taken.

PCl_5(g) ⇌ PCl_3(g) + Cl_2(g)

The experiment is repeated with one mole of phosphorus(V) chloride heated to 600 K in a sealed flask of volume 2 dm³.

How will the measurements vary?

the equilibrium concentrations of PCl_3(g) and Cl_2(g) are higher in the second experiment

the equilibrium concentration of PCl_5(g) is lower in the second experiment

the equilibrium concentrations of all three gases are the same in both experiments

the value of the equilibrium constant is higher in the second experiment

Question 3

Two moles of compound P were placed in a vessel. The compound P was partly decomposed by heating. A dynamic equilibrium between chemicals P, Q and R was established.

At equilibrium, x mol of R were present and the total number of moles present was (2 + x).

What is the equation for this equilibrium?

P ⇌ 2Q + R

2P ⇌ 2Q + R

2P ⇌ Q + R

2P ⇌ Q + 2R

Question 4

Sulfur trioxide is manufactured from sulfur dioxide and oxygen, using the Contact process.

Which condition affects the value of the equilibrium constant, K_c?

adjusting the temperature

increasing the pressure

removing SO₃ from the equilibrium mixture

using a catalyst

Question 5

Nitrogen reacts with hydrogen to produce ammonia.

N₂(g) + 3H₂(g) 2NH₃(g)

A mixture of 2.00 mol of nitrogen, 6.00 mol of hydrogen, and 2.40 mol of ammonia is allowed to reach equilibrium in a sealed vessel of volume 1 dm³ under certain conditions. It was found that 2.32 mol of nitrogen were present in the equilibrium mixture.

What is the value of K_c under these conditions?

2.32×(6.96)3(1.76)2

2.32×(6.32)3(1.76)2

2.32×(6.32)3(2.08)2

2.32×(6.00)3(2.40)2

Question 6

The value of the equilibrium constant, K_c , for the reaction to form ethyl ethanoate from ethanol and ethanoic acid is 4.0 at 60°C.

C₂H₅OH + CH₃CO₂H ⇌ CH₃CO₂C₂H₅ + H₂O

1.0 mol of ethanol and 1.0 mol of ethanoic acid are allowed to reach equilibrium at 60°C.

What is the number of moles of ethyl ethanoate formed?

31 mol

32 mol

41 mol

43 mol

Question 7

The reaction between sulfur dioxide and oxygen is reversible.

2SO_2(g) + O_2(g) ⇌ 2SO_3(g) K_c = 280 mol^-1dm³ at 1,000 K

In an equilibrium mixture at 1,000 K the sulfur trioxide concentration is 6.00 mol dm^-3.

The sulfur dioxide concentration is twice the oxygen concentration.

What is the sulfur dioxide concentration?

0.175 mol dm^-3

0.254 mol dm^-3

0.318 mol dm^-3

0.636 mol dm^-3

Question 8

0.200 mol of sulfur dioxide and 0.200 mol of oxygen are placed in a 1.00 dm³ sealed container.

The gases are allowed to react until equilibrium is reached.

2SO₂ + O₂ ⇌ 2SO₃

At equilibrium there is 0.100 mol of SO₃ in the container.

What is the value of K_c?

0.150 mol dm^-3

0.800 mol dm^-3

1.25 mol dm^-3

6.67 mol dm^-3

Question 9

Which statement about the effect of a catalyst on a reversible reaction is correct?

the activation energy of the forward reaction stays the same

the composition of the equilibrium mixture stays the same

the rate of the backward reaction stays the same

the value of the equilibrium constant changes

Question 10

This question is about the reversible reaction below.

2NO_2(g) ⇌ N₂O_4(g)

A chemist investigating this reaction started with 10 moles of NO₂ and allowed the system to reach equilibrium. If 3 moles of N₂O₄ are formed, the number of moles of NO₂ at equilibrium is

8.5

Question 11

Chloroethene, CH₂=CHCl, is prepared in the presence of a solid catalyst using the equilibrium reaction below.

CH₂ClCH₂Cl_(g) ⇌ CH₂=CHCl_(g) + HCl_(g) ΔH = +51 kJ mol^-1

Which change would result in an increased equilibrium yield of chloroethene?

increasing the pressure

increasing the surface area of the catalyst

increasing the temperature

use of a homogeneous catalyst

Question 12

Hydrogen gas can be produced as shown below.

CH_4(g) + H₂O_(g) ⇌ CO_(g) + 3H_2(g) ΔH = +206 kJ mol^-1

Which conditions produce the greatest equilibrium yield of hydrogen?

low temperature and high pressure

low temperature and low pressure

high temperature and high pressure

high temperature and low pressure

Question 13

A pale brown mixture of NO₂ and N₂O₄ is allowed to reach equilibrium in a sealed gas syringe according to the following equation.

2NO_2(g) ⇌ N₂O_4(g)

When the plunger is pushed further into the syringe the pressure increases and the mixture becomes paler in colour.

When the syringe is placed in a hot oven the mixture becomes darker in colour.

Which of the following statements is correct?

NO₂ is brown and the forward reaction is exothermic

NO₂is brown and the forward reaction is endothermic

NO₂is colourless and the forward reaction is exothermic

NO₂is colourless and the forward reaction is endothermic

Question 14

Which statement is not always correct for a reaction at equilibrium?

reactants ⇌ products

the concentrations of the reactants and products are equal

the equilibrium can be achieved starting from the reactants

the equilibrium can be achieved starting from the products

the rate of the forward reaction is equal to the rate of the

reverse reaction