activation energy
Catalysts interact with reactants so the reaction can occur by an alternate pathway that has a lower activation energy. Activation energy is the energy needed to start a reaction. When activation energy is lower, more reactant particles have enough energy to react so the reaction goes faster. Many catalysts work like the one in the Figure below . You can see an animated version at the following URL. The catalyst brings the reactants together by temporarily bonding with them. This makes it easier and quicker for the reactants to react together. Notice how the catalyst is released by the product molecule at the end of the reaction.