What defines a catalyst?

A catalyst is defined as a substance that increases the rate of a chemical reaction without being consumed in the process. This means that at the end of the reaction, the catalyst remains unchanged and can continue to facilitate subsequent reactions. The unique property of a catalyst allows it to participate in the reaction without altering its own chemical structure, enabling it to be reused multiple times.

In this context, the other answers do not accurately describe what a catalyst does. A catalyst does not slow down a reaction; instead, it accelerates the reaction. It is also not a substance that gets used up, as a catalyst remains available for further reactions after facilitating the initial one. Unlike a reactant, which is required for the reaction and is consumed during the process, a catalyst works by providing an alternative pathway for the reaction with a lower activation energy, thereby enhancing the reaction rate while remaining intact.