How does a catalyst work?
4 marks · NormalThe diagram below shows the reaction profile for a chemical reaction without a catalyst.
Draw on the diagram, using a dashed curve, how the reaction profile would look if a catalyst was used.
Explain, using the diagram, how the catalyst affects the reaction.
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(a) — · must show Dashed curve begins at reactants and ends at products (same as provided profile)., Dashed curve has a lower peak than the original solid curve., Dashed curve shape indicates a lower activation energy for the catalysed pathway.
(b) A catalyst provides an alternative pathway for the reaction that requires less energy to reach the peak (lower activation energy), shown as a lower curve on the diagram. However, the difference in energy between reactants and products stays the same.
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Marking points
M1 (a) · 1 mark · Draws a dashed curve from reactants to products with a lower peak (lower activation energy), maintaining the same start and end points.
A1 (a) · 1 mark · Correctly labels or indicates the dashed curve as the catalysed pathway.
B1 (b) · 1 mark · Explains that the catalyst lowers the activation energy, as shown by the lower peak.
B2 (b) · 1 mark · States that the overall energy change (difference between reactants and products) does not change.
Worked solution
On the diagram, the dashed curve shows the catalysed pathway with a lower activation energy.
Explanation: The catalyst provides an alternative route with a lower peak. This represents a lower activation energy, so the reaction is easier to start. The energy difference between reactants and products (overall energy change) does not change.