How does a catalyst work?
3 marks · NormalA student claims, "A catalyst lowers the energy of the reactants."
Discuss whether this statement is correct, using ideas from reaction profile diagrams and activation energy.
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The statement is incorrect. A catalyst does not lower the energy of the reactants; it provides an alternative pathway with lower activation energy. On a reaction profile diagram, the reactants' and products' energies stay the same, only the peak for activation energy is lower with a catalyst.
Also accept: The catalyst provides a different path with lower activation energy, but does not affect the energy level of reactants or products.
Common mistakes: Saying a catalyst changes the energy of reactants or products
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Marking points
B1 · 1 mark · States that the claim is incorrect (or disagrees).
B2 · 1 mark · Explains that a catalyst provides an alternative reaction pathway of lower activation energy (not lowering reactants' energy).
B3 · 1 mark · Mentions that reactants' and products' energies remain unchanged on the reaction profile diagram; only the activation energy peak is lower.
Worked solution
The statement is not correct. A catalyst does not lower the energy of the reactants. Instead, it provides an alternative reaction pathway that has a lower activation energy. In a reaction profile diagram, the energy of the reactants and products remains the same whether or not a catalyst is used, but the activation energy (the height of the peak) is lower for the catalysed reaction.