What are catalysts?
2 marks · EasyExplain why a catalyst is not included in the balanced chemical equation for a reaction, even though it is present and important during the reaction.
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Because the catalyst is not chemically changed or used up, so its amount does not change over the course of the reaction.
Also accept: It is unchanged at the end of the reaction.; It is not part of the reactants or products.
Common mistakes: Saying the catalyst is not important.; Including it on one side of the equation.
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Marking points
M1 · 1 mark · States that the catalyst is not changed/used up by the reaction.
A1 · 1 mark · States that the catalyst does not appear as a reactant or product in the equation.
Worked solution
A catalyst is not included in the balanced chemical equation because it is not consumed or chemically changed in the reaction. Its amount is the same at the end as at the start, so it does not count as a reactant or a product.