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AQA · GCSE · Chemistry · Higher

Catalysts and equilibrium position

Q05.5 2 marks

Sulfur dioxide (SO₂) reacts reversibly with oxygen (O₂) to produce sulfur trioxide (SO₃):

2 SO2(g)+O2(g)⇌2 SO3(g)2\,SO_2(g) + O_2(g) \rightleftharpoons 2\,SO_3(g)

A catalyst is used in the reaction.

Suggest what effect the catalyst has on the position of the equilibrium. Give one reason for your answer.

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Marking points

  1. 1 Effect: states that the equilibrium position does not change.
  2. 2 Reason: states that the forward and reverse reaction rates increase equally.

Full-mark answer

Effect: the equilibrium position does not change. Reason: the catalyst increases the rates of the forward and reverse reactions equally.

Why this answer loses marks

The catalyst shifts the equilibrium towards the products.

A catalyst speeds the forward and reverse reactions equally, so it does not change the equilibrium position.

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