A chemical reaction involves the conversion of reactants into product. In the course of chemical reaction a new chemical bonds are formed by breaking the already existing bonds; thus, releasing or absorbing the energy.
A reaction that occurs on its own without the supply of external energy is called spontaneous reaction. A non-spontaneous chemical reaction needs the supply of external energy. However, not every spontaneous reaction occurs on its own. Some need the supply of activation energy to activate the reaction.
This energy helps the reactants to cross the energy barrier and get converted into the products. Such type of required energy is called as Energy of activation. Once the sufficient amount of activation energy is supplied to the reaction, it will occur on its own until it is completed.
Hence, the activation energy plays a very important role in reaction completion and product formation.