What is activation energy?

• Activation energy, E_a is the minimum energy required for substances to react. It represents the energy barrier that has to be overcome before a reaction can take place to form products.
• In a reaction, the reactant molecules come together and chemical bonds are stretched, broken, and formed in producing the products.
• During this process the energy of the system increases to a maximum, then decreases to the energy of the products.
• The activation energy is the difference between the maximum energy and the energy of the reactants; i.e. it is the energy barrier that has to be overcome for the reaction to proceed.
• The activation energy determines the way in which the rate of the reaction varies with. It is usual to express activation energies in joules per mole of reactants.