What is the definition of a catalyst in a chemical reaction?

A catalyst is defined as a substance that changes the rate of a chemical reaction without being consumed in the process. This means that while a catalyst may facilitate a reaction, it is not permanently altered or used up by that reaction, allowing it to participate repeatedly.

In contrast to the other options, a catalyst does not increase the reaction time; instead, it often speeds up the reaction. It also is not a product of the chemical reaction, which is typically formed as a result of the reactants being converted into different substances. Thus, the defining feature of a catalyst is that it remains unchanged at the end of the reaction, enabling it to be used again in future reactions, which is captured in the correct answer.