Exothermic reactions- When we observe that from any reaction a high amount of heat is evolved. This makes the reaction mixture warm. Reaction in which heat is released along with the formation of products are called exothermic reactions.

Example- Burning of natural gas, respiration, decomposition of vegetable matter into compost.

Endothermic reactions- If we observe that while performing any reaction if any form of energy is absorbed or required either as heat, light or electricity for breaking or making the reactants. So reactions in which any form of energy is absorbed are known as endothermic reactions.