In a chemical process, which statement best describes a catalyst?

• A. A reactant that is consumed in the reaction
• B. A product formed at the end of the reaction
• C. A substance that slows down the reaction
• D. A substance that speeds up the reaction without being consumed

Answer: (D)

A catalyst speeds up a chemical reaction without being consumed in the process. It does this by providing an alternative reaction pathway that has lower activation energy, so more reactant molecules can react in the same amount of time. Since it isn’t used up, the catalyst remains unchanged after the reaction and can continue to catalyze additional reactions. This is why describing a catalyst as a substance that speeds up the reaction without being consumed is the most accurate. In contrast, describing the substance as a reactant would imply it is consumed, which it isn’t; describing it as a product would mean it’s produced rather than used to drive the reaction; and describing it as something that slows down the reaction would refer to an inhibitor, not a catalyst.