What characteristic distinguishes a catalyst from a reactant?

A catalyst is distinct from a reactant primarily because it remains unchanged after the reaction occurs. This means that catalysts can participate in the reaction process, aiding in the transformation of reactants into products without being consumed or altered in the process. They lower the activation energy required for the reaction, which speeds up the reaction rate, but once the reaction is complete, the catalyst is available to facilitate other reactions.

In contrast, reactants are substances that are consumed during the chemical reaction to form products. They undergo chemical change and are transformed into new substances, whereas catalysts act to enhance the reaction without undergoing a permanent change themselves. This fundamental characteristic of retaining their original structure and function after the reaction is what sets catalysts apart from reactants in chemical reactions.