What is a catalyst?

A catalyst is specifically defined as a substance that increases the rate of a chemical reaction without being consumed or permanently altered by the reaction itself. This means that while a catalyst facilitates the transformation of reactants into products by lowering the activation energy required for the reaction, it can be reused multiple times. This characteristic allows catalysts to play vital roles in various processes, including industrial applications and biological functions, where enzymes act as biological catalysts.

Other options do not accurately reflect the definition of a catalyst. A substance that can be consumed in a reaction does not describe a catalyst's purpose, as catalysts remain unchanged. Additionally, while some reactions may occur at room temperature, this is not relevant to the definition of a catalyst. Finally, not all catalysts generate heat during the reactions they accelerate, and many do not have any direct thermal effect. Therefore, the correct choice emphasizes the primary role of catalysts in speeding up chemical reactions.