How does a catalyst work?
5 marks · HardA student draws the following reaction profile diagram for a certain chemical reaction:
Use the diagram to answer the questions below.
State the term used for the energy difference from the reactants up to the peak without a catalyst.
Describe how the diagram shows the effect of a catalyst on the reaction.
Explain why many more particles in the reaction mixture can react when a catalyst is used, referring to the activation energy.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Activation energy
(b) The catalyst provides an alternative pathway that has a lower peak (activation energy) than the uncatalysed route, shown in the diagram by the lower (dashed) curve.
(c) Lowering the activation energy means more particles have enough energy to react when they collide, so more collisions are successful with a catalyst.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States 'activation energy' as the energy difference from reactants to peak (without a catalyst).
B2 (b) · 1 mark · Identifies catalyst effect as lowering activation energy/providing alternative pathway in the diagram.
B3 (b) · 1 mark · Describes how the lower/dashed curve represents the catalyst pathway.
B4 (c) · 1 mark · Explains lowering activation energy increases the number of particles able to react.
B5 (c) · 1 mark · Correctly links to more successful collisions occurring due to catalyst.
Worked solution
a) The term for this energy difference is activation energy.
b) The diagram shows two energy pathways: the normal (higher peak) and the catalysed (lower, dashed peak). The catalyst offers an alternative pathway with a lower activation energy, seen as the lower peak.
c) Many more particles can react with a catalyst because the activation energy is now lower; more particles in the mixture will have energy equal to or greater than this lower activation energy, allowing more successful collisions.