Exothermic reaction: Exothermic reaction is the reaction where heat energy evolves.
C (graphite) + O2 → CO2; ∆H298K = – 393.4 Kj mol-1
Endothermic reaction: Endothermic reaction is the reaction where heat energy absorbed.
CaCO3 (s) —∆→ CaO(s) + CO2 (g); ∆H298K = + 178 Kj mol-1
In endothermic reaction the value of ∆H is positive.