Define Exothermic Reaction and Endothermic Reaction

Exothermic reaction: Exothermic reaction is the reaction where heat energy evolves.

C (graphite) + O₂ → CO₂; ∆H_298K = – 393.4 Kj mol^-1

Endothermic reaction: Endothermic reaction is the reaction where heat energy absorbed.

CaCO₃ (s) —∆→ CaO(s) + CO₂ (g); ∆H_298K = + 178 Kj mol^-1

In endothermic reaction the value of ∆H is positive.