Question

What are exothermic and endothermic reactions? Give examples.

Answer 1

Exothermic reactions: Those reactions in which heat is evolved are known as exothermic reactions. An exothermic reaction is indicated by writing “+ Heat” on the product's side of an equation
Example:
(i) $C\left(s\right)+O_2\left(g\right)\to C{P}_2\left(g\right)+\text{Heat}$
(ii) $N_2\left(g\right)+3H_2\left(g\right)\to 2N{H}_3\left(g\right)+\text{Heat}$
Endothermic reactions: Those reactions in which heat is absorbed are known as endothermic reactions. An endothermic reaction is usually indicated by writing “– Heat” on the product side of a chemical equation
(i) $C\left(s\right)+2S\left(s\right)\to C{S}_2\left(I\right)-\text{Heat}$
(ii) $N_2\left(g\right)+O_2\left(g\right)\to 2NO\left(g\right)-\text{Heat}$