Question

Write a short note on,
-Threshold energy
-Energy of activation

Answer 1

Threshold energy and energy of activation are two terms associated with kinetics of a reaction. The minimum energy required for a reaction is threshold energy and the excess energy required to acquire threshold energy is energy of activation.

Complete step by step answer:
-Rate of a reaction is affected by temperature, concentration of reactant, nature of reactant and presence of catalyst. According to collision theory, a reaction takes place as a result of effective collision between the reactant molecules. For effective collision, the reactant molecules should possess a minimum energy. This energy is called threshold energy. But the energy of most of the molecules will be less than the threshold energy. So we need to provide a certain amount of energy to the reactant molecules. This excess energy needed to activate the reactant molecule is called the energy of activation or activation energy.
-Threshold energy = energy of activation + average initial kinetic energy of reactants
-Activation energy is different for endothermic and exothermic reactions. Energy of products will be higher than that of reactants for endothermic reaction. In an exothermic reaction, the energy of products will be less than that of reactants.
When we add catalysts to a reaction, the rate of reaction increases. Catalyst increases rate of reaction by lowering the activation energy of the reaction.

Note:
Activation energy is the energy barrier that a molecule should overcome for a reaction to take place. Threshold energy is always higher than the activation energy. Usually, reactions of low activation energy are faster and reactions of higher activation energy are slower.