Topic 7/17 - Equilibrium

Which of the following is a property of a system at equilibrium?

• The concentrations of reactants and products are equal.

• The rate of the forward reaction is zero.

• The rate of the forward reaction is equal to the rate of the reverse reaction.

• The rate of the reverse reaction is a maximum.

Consider the reaction:

CO₂(g) + 4H₂(g) ↔ CH₄(g) + 2H₂O(g)

What is the expression for the equilibrium constant?

• A

• B

• C

• D

In which system will decreasing the pressure increase the equilibrium concentration of the species in bold?

• A

• B

• C

• D

What is the effect of increasing the temperature on the position of equilibrium and the value of the equilibrium constant for the reaction:

CO(g) + 3H₂(g) ↔ CH₄(g) + H₂O(g) ΔH = -206 kJ mol^-1

• A

• B

• C

• D

Consider the system: A(g) ↔ B(g)

What is the effect of introducing a catalyst?

• The rate of the forward reaction increases but the rate of the reverse reaction remains the same.

• The position of equilibrium is shifted to the right.

• The time taken to reach equilibrium is decreased.

• The value of the equilibrium constant is reduced.

Which of the following changes will increase the equilibrium yield of ammonia according to the following equation?

N₂(g) + 3H₂(g) ↔ 2NH₃(g) ΔH = -92 kJ mol^-1

• decreasing the temperature from 200°C to 100°C

• introducing a catalyst

• decreasing the pressure from 200 atm to 100 atm

• increasing the temperature from 100°C to 200°C

(HL only) The equilibrium concentrations at a certain temperature for the reaction

2SO₂(g) + O₂(g) ↔ 2SO₃(g)

are 0.20 mol dm^-3 for [SO₂], 0.40 mol dm^-3 for [O₂], 0.80 mol dm^-3 for [SO₃].

The value of the equilibrium constant at this temperature is:

• 0.025

• 2

• 10

• 40

(HL only) Consider the equilibrium:

A(g) + X(g) ↔ 2Z(g)

0.20 mol Z are placed in a sealed 10 dm³ container and allowed to come to equilibrium at 500 K. At equilibrium, 0.040 mol X were present in the reaction vessel. The value of the equilibrium constant at this temperature is:

• 5

• 9

• 16

• 25

Consider the reversible reaction N₂(g) + 3H₂(g) ↔ 2NH₃(g).

The value of the equilibrium constant at certain temperature, T, is 2.0.

Given the following concentrations in the reaction mixture, which of the following is correct?

• Q = 0.50 and the system is not at equilibrium.

• Q = 1.3 and the system is not at equilibrium.

• Q = 2.0 and the system is at equilibrium.

• Q = 2.0 and the system is not at equilibrium.

Which of the following describes the relationship between the change in Gibbs free energy, ΔG, and the equilibrium constant, K?

• If K > 1 then ΔG > 0.

• If K = 0 then ΔG = 0.

• If K < 1 then ΔG < 0.

• If K > 1 then ΔG < 0.