What are exothermic and endothermic chemical reactions?

Explanation

Exothermic reaction : Those reactions in which heat is evolved during the reaction are called exothermic reaction.
Ex Burning of coal.
` C(s) + O_2(g) to CO_2 (g) + ` Heat
Endothermic reaction : Those reactions in which heat is absorbed during the reaction are called endothermic reactions.
Ex: Decomposition of lime stone
` CaCO overset("heat")(to) CaO(s) + CO_2 (g)`