What is the effect of a catalyst on a reaction?

• A. A catalyst is consumed in the reaction.
• B. A catalyst provides an alternative pathway with lower activation energy, increasing rate without being consumed.
• C. A catalyst changes the products formed.
• D. A catalyst has no effect on reaction rate.

Answer: (B)

The main idea is that a catalyst creates an alternative reaction pathway with a lower activation energy, so more molecules have enough energy to react at the same temperature and the reaction goes faster. It isn’t consumed in the process, so it can go on catalyzing again and again. Because it speeds up the forward and, in a reversible reaction, the reverse equally, it doesn’t change the final amounts of products—just how quickly equilibrium is reached. If a catalyst were consumed, or if it changed what products were formed, or if it had no effect on rate, those would not describe what a catalyst does.