What is a Catalyst?

A catalyst decreases the activation energy of a chemical reaction. Catalysts participate in reactions but are neither reactants nor products of the reaction they catalyze. An exception is the process of autocatalysis where the product of a reaction helps to accelerate the same reaction. They work by providing an alternative pathway for the reaction to occur, thus reducing the activation energy and increasing the reaction rate. More generally, one may at times call anything that accelerates a reaction, without itself being consumed or changed, a "catalyst" (for example, a "catalyst for political change").