Exothermic : In this heat is evolved during the reaction.

(i) Oxidation of methane in presence of air
CH4(g) + 202(g) → CO2(g) + 2H2O(l) + 890.0 kJ
(ii) Formation of sulphur trioxide
2SO2 + O2 →2SO3 + 46.9 kcal.
(iii) Oxidation of ammonia


Endothermic reaction: In this heat supplied to reaction to complete .
(i) Formation of hydrogen iodide
H2(g) + l2(g) → 2HI(g) – 51.9 kJ
(ii) Decomposition of calcium carbonate
CaCO3(s) → CaO(s) + CO2(g) – 177.8 kJ
(iii) Formation of carbon disulphide
C(s) + 2S(s) → CS2(l) – 92 kJ.