Why are enzymes considered to be catalyst of reaction?
Because they lower the activation energy needed to start a reaction
Activation energy is the minimum amount of energy that is needed for reactions to occur. It may take years for some reactions to acquire a sufficient amount of activation energy, so catalysts are used to speed up these reactions. These catalysts lower the activaiton energy that the reaction would require. In other words, they make it possible for a reaction to occur sooner because less energy is needed to trigger it.