Specification Point 3.21C (Paper 2C Only):
Understand why a catalyst does not affect the position of equilibrium in a reversible reaction

Catalyst: A substance that increases the rate of a reaction, but is chemically unchanged at the end of the reaction.

Position of equilibrium: the concentration of reactant and products at the equilibrium state.

  • When the position of equilibrium shifts to the left, it means the concentration of reactant increases.
  • When the position of equilibrium shifts to right, this means the concentration of product increases.

Effect of Catalyst on Equilibrium Position

Effect of catalyst on equilibrium position:

  • A catalyst will not affect the position of equilibrium
  • This is because the catalyst increases the rate of both the forward and backward reactions by the same amount (by providing an alternative pathway requiring lower activation energy)
  • As a result, the concentration of reactants and products is nevertheless the same at equilibrium as it would be without the catalyst

Diagram:

Effect of catalyst on equilibrium position, CIE IGCSE Chemistry

The effect of catalyst on equilibrium position

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.