Adding a catalyst
2 marks · NormalExplain why adding a catalyst does not change the position of equilibrium in a reversible reaction.
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Also accept: Catalyst increases the rate of both reactions the same amount, so the ratio of products to reactants stays the same; It only allows equilibrium to be reached faster, not shifting it; No net change in concentrations at equilibrium
Common mistakes: Saying a catalyst speeds up only the forward reaction; Saying a catalyst increases the yield
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Marking points
M1 · 1 mark · States or clearly implies that a catalyst increases the rate of both the forward and backward (reverse) reactions equally.
A1 · 1 mark · Clearly states or implies that a catalyst does not change/shifts the position of equilibrium.
Worked solution
A catalyst increases the rate of both the forward and backward reactions by the same amount.
Therefore, the relative concentrations at equilibrium do not change, so the position of equilibrium does not shift.