A substance that lowers activation energy without being consumed is called

• A. Inhibitor
• B. Enzyme
• C. Catalyst
• D. Reactant

Answer: (C)

A catalyst lowers the activation energy of a reaction by providing an alternative pathway with a lower energy barrier, and it is not consumed in the process, so it can act again and again to increase the reaction rate. This is exactly what the phrase describes: the substance speeds up the reaction without being used up. Enzymes are a special case of catalysts found in biology, doing the same job for biochemical reactions. Inhibitors, on the other hand, slow or stop reactions by interfering with the process rather than lowering the energy barrier. A reactant is simply a starting material that gets transformed and is consumed.