Equilibrium

Question 1

Explain what is happening when a reaction reaches a ‘dynamic equilibrium’.

Answer 1

• The forward reaction will be going at the same rate as the backward reaction.
• The amounts of reactants and products won’t be changing any more.

Question 2

Describe how changing the temperature affects the equilibrium position of a reversible reaction where the forward reaction is exothermic.

Answer 2

Increasing the temperature shifts the equilibrium in the exothermic (positive ΔH) direction to try to replace the heat.

Question 3

What type of reactions can reach a dynamic equilibrium?

Answer 3

Reversible reactions.

Question 4

If the Kc value is greater than 1:

• The equilibrium will move to the ____.
• There will be more _______ than _______ present at equilibrium.

Answer 4

If the Kc value is greater than 1:

• The equilibrium will move to the right.
• There will be more products than reactants present at equilibrium.

Question 5

If the Kc value is less than 1:

• The equilibrium will move to the ____.
• There will be more _______ than _______ present at equilibrium.

Answer 5

If the Kc value is less than 1:

• The equilibrium will move to the left.
• There will be more reactants than products present at equilibrium.

Question 6

Dichromate(VI) ions and water were mixed together and allowed to reach equilibrium at a fixed temperature:
Cr₂O₇²⁻ (aq) + H₂O (l) ⇄ 2CrO₄²⁻ (aq) + 2H⁺ (aq)
Write an expression for Kc for this reaction.
[1 mark]

Answer 6

[CrO₄ ²⁻]² [H⁺]²

[Cr₂O₇²⁻] [H₂O]

Question 7

Dichromate(VI) ions and water were mixed together and allowed to reach equilibrium at a fixed temperature:
Cr₂O₇²⁻ (aq) + H₂O (l) ⇄ 2CrO₄²⁻ (aq) + 2H⁺ (aq)

What would happen to the value of Kc if the concentration of water increased? Explain your answer.
[1 mark]

Answer 7

There would be no change as the concentrations of the other reagents would change to keep Kc constant.