Semmelweis Chemistry Entrance Practice Exam

A catalyst is a substance that accelerates the rate of a chemical reaction by providing an alternative pathway with a lower activation energy for the reaction to occur. Importantly, a catalyst is not consumed in the process; it can participate in the reaction and then be regenerated, meaning it can be used repeatedly. This characteristic is crucial in various chemical processes, including industrial reactions and biological systems such as enzyme-catalyzed reactions.

In contrast, reactants are the starting materials that undergo transformation during a chemical reaction, while products are the substances formed as a result of that reaction. An inhibitor, on the other hand, slows down or prevents a chemical reaction from occurring, which is the opposite of what a catalyst does. Therefore, the definition of a catalyst as a substance that increases the reaction rate without being consumed fits perfectly, making it the correct choice.