Adding a catalyst
3 marks · NormalA teacher tells her class that adding a catalyst to a reversible reaction will make the equilibrium mixture contain more products. Is she correct? Explain your reasoning.
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No, she is not correct. Adding a catalyst increases the speed at which equilibrium is reached, but does not affect the amounts of products or reactants at equilibrium, because it speeds up both the forward and reverse reactions equally.
Also accept: No; the catalyst does not change the equilibrium position or the yield; No; the ratio of products to reactants at equilibrium stays the same
Common mistakes: Saying a catalyst increases the amount of product at equilibrium; Ignoring effect on both directions
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Marking points
M1 · 1 mark · States (or implies) the teacher is not correct / denies the claim.
M2 · 1 mark · Mentions that catalyst increases the rates of both forward and reverse reactions equally.
A1 · 1 mark · States that the positions of equilibrium or amounts at equilibrium do not change.
Worked solution
No, the teacher is not correct. Adding a catalyst increases the rate of both the forward and reverse reactions equally, so it does not change the ratio of products and reactants at equilibrium. The only effect is to make equilibrium be reached faster; the composition at equilibrium stays the same.