What is the term for a substance that lowers activation energy but is not consumed in a reaction?

• A. Activated complex
• B. Rate Law
• C. Catalyst
• D. Reaction coordinate diagram

Answer: (C)

A catalyst is a substance that provides an alternative pathway for a reaction with a lower activation energy, allowing the reaction to proceed more quickly without the catalyst itself being consumed. Because it is regenerated at the end of the reaction, its amount remains unchanged and it can catalyze multiple cycles. This lowers the energy barrier the reactants must overcome, which, by the Arrhenius relationship, increases the rate constant and speeds up the reaction without altering the final equilibrium composition. For example, enzymes act as biological catalysts by lowering Ea for specific metabolic steps, and manganese dioxide catalyzes the decomposition of hydrogen peroxide. The activated complex is the high-energy transition state along the path, a fleeting arrangement, not a substance; a rate law describes how the rate depends on concentrations; a reaction coordinate diagram illustrates energy changes, not a material that speeds things up.