When the heat from outside is absorbed during some physical changes such as melting of ice or dissolution of potassium nitrate in water, it is called ‘Endothermic processes.’ During the process of endothermic chemical reactions heat is either absorbed from the surroundings or has to be supplied continuously from outside.
CaCO3 (s) + heat → CaO (s) + CO2(g) (Endothermic Reaction)