What does an enzyme do in a chemical reaction?
It speeds it up.
An enzyme acts as a catalyst by providing an alternate pathway for the reaction that may have a lower the activation energy. If the activation energy of the reaction pathway is lower, more reactant particles have the necessary energy to form activated complexes at a given energy level, which makes the reaction proceed completion quicker.
If the reaction is in equilibrium, a catalyst will speed up the rate of the forward reaction and the reverse reaction equally, also a catalyst in no way changes the amount of product yielded as that remains the same.
A catalyst or enzyme is not used up in the reaction, and can reused for other reactions.
Enzymes are catalysts.
A catalyst is a substance which speeds up a chemical reaction but remains unchanged itself at the end. Thus, enzymes alter the rates of chemical reactions without themselves being chemically changed at the end of the reaction.
They speed up a chemical reaction by lowering the activation energy barrier required to start a reaction.