Glossary
catalyst
A catalyst speeds up a reaction by lowering the energy it needs, and it is not used up by the reaction.
A catalyst is a substance that speeds up a reaction without being consumed by it. It works by lowering the energy the reaction needs to get started, so the same reaction runs faster at the same temperature. Because it is not used up, a small amount can speed up a large reaction, and you can often recover it unchanged afterward. A catalyst changes only the rate of a reaction, never how much product forms — that is set by how much reactant you started with. The common error is to think a catalyst is used up like a reactant, or that it makes more product; it only makes the reaction go faster.
Taught in
Related terms
- exothermic — An exothermic reaction releases energy as heat (and often light); an endothermic reaction takes energy in and cools its surroundings.
Source: OpenStax Chemistry 1e and Chemistry: Atoms First 1e, first editions (CC BY 4.0). Each definition restates the Chemistry guide in this exam, which carries the per-source citations on its own page. (OpenStax 1e accessed 2026-10-08)