What is meant by the EA of a reaction? How do enzymes affect the EA and the DG of a reaction?

Activation energy may be defined as the minimum amount of the energy required to convert the substrate into the product. The higher the activation energy of a reaction, the slower the speed of a reaction.

The enzymes decreases the activation energy of the reaction and increases the effective collision between the substrate. The enzymes does not change the DG (delta G) or free energy of the reaction. The enzymes maintain the equilibrium of the reaction by increasing the equal amount of the forward and backward rate of the reaction.