Adding a catalyst
4 marks · NormalThe decomposition of hydrogen peroxide is a reversible reaction represented by the following equation:
State what effect, if any, adding a catalyst will have on the rates of the forward and reverse reactions.
Explain how the catalyst affects the time taken to reach equilibrium.
Does adding a catalyst change the position of equilibrium for this reaction? Explain your answer.
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(a) It increases the rates of both the forward and reverse reactions equally.
(b) It decreases the time taken to reach equilibrium / the reaction reaches equilibrium faster.
(c) No, adding a catalyst does not change the position of equilibrium because it increases the rate of both reactions equally. · must show States 'no' or equivalent denial, Correct reasoning (no change in equilibrium composition, both directions sped up equally)
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Marking points
B1 (a) · 1 mark · States that catalyst increases the rate of both forward and reverse reactions equally.
B2 (b) · 1 mark · States that equilibrium is reached faster / time to reach equilibrium decreases.
M1 (c) · 1 mark · States that the position of equilibrium does not change.
A1 (c) · 1 mark · Gives correct explanation (catalyst affects both reactions equally / does not change equilibrium concentrations).
Worked solution
a) Adding a catalyst increases the rates of both the forward and reverse reactions equally.
b) This means that equilibrium is established faster, so the reaction reaches equilibrium in less time.
c) No, adding a catalyst does not change the position of equilibrium because it increases the rates of both the forward and backward reactions by the same amount. The relative concentrations of reactants and products remain unchanged at equilibrium.