Activation energy

The activation energy of a reaction is the minimum energy requirement for a successful collision to occur.  All chemical reactions have an intermediate transition state that is at a higher energy than the reactants. This transition state must be reached and overcome before the product can be reached.  This energy can be lowered through the use of a catalyst or an enzyme via the creation of a lower second transition state. This means that a catalyst can make a reaction appear to occur faster, as more molecules will have energy greater than activation energy (second transition state), therefore there are more successful collisions per second.