A substance that lowers the activation energy and speeds up a reaction without being consumed is a

• A. Catalyst
• B. Spectator Ion
• C. Oxidation
• D. Reduction

Answer: (A)

Think about activation energy—the energy barrier that must be overcome for reactants to convert to products. A catalyst provides an alternative pathway with lower activation energy, so more collisions have enough energy to react at the same temperature. Because it isn’t consumed in the reaction, it can speed up the process over and over again. A spectator ion, while present in solution, doesn’t participate in the chemical change and thus doesn’t alter the energy barrier. Oxidation and reduction refer to electron-transfer changes, not to a substance that lowers the energy barrier or is used up in the reaction.