The decomposition reactions are endothermic reactions. The reactions I2(g)→2I(g) and HCl(g)→H(g)+Cl(g) are decomposition reactions. The heat vaporisation is an endothermic reaction. Hence, the conversion of H2O(l)→H2O(g) is endothermic process. The heat of combustion is an exothermic process. The heat involved in C(s)+O2(g)⟶CO2(g) is heat of combustion. The dissolution of ammonium chloride in water is an endothermic process. NH4Cl(s)→NH4+(aq)+Cl−(aq);ΔH=+15.1kJ/mol.