Question

Define exothermic and endothermic changes.

Answer 1

(1) Exothermic change : Reactions accompanied with release of heat are called exothermic reactions.

Example of exothermic reaction:

All burning reactions are exothermic. When carbon burns in air, heat is released.

$\mathrm{C}+{\mathrm{O}}_2\to {\mathrm{CO}}_2+\mathrm{Heat}$

(2) Endothermic Change: Reactions accompanied with absorption of heat are called endothermic reactions.

Example of endothermic reaction:

When carbon and sulphur are heated,they react to form carbon disulphide. Heat is absorbed in the reaction.

$\mathrm{C}+2\mathrm{S}+\mathrm{Heat}\to {\mathrm{CS}}_2$