What is a substance that initiates or accelerates a chemical reaction without itself being affected?

A catalyst is a substance that initiates or accelerates a chemical reaction while remaining unchanged at the end of the reaction. This means that it can participate in the reaction by lowering the activation energy required for the reaction to proceed, but it does not get consumed in the process. As a result, a catalyst can continue to facilitate multiple reactions without needing to be replenished.

In addition to catalyzing reactions, catalysts are crucial in various industrial processes and biological systems. For example, in biological systems, enzymes function as biological catalysts to speed up metabolic reactions, but they are specific types of catalysts. The term "substrate" refers to the reactant molecule upon which an enzyme acts, and a "compound" is a broader term for a chemical substance formed from two or more elements. Therefore, while all these terms relate to chemistry, a catalyst specifically denotes the role of accelerating reactions without being altered.