Heat is absorbed during the reaction. Chemical reactions in which, during the formation of chemical compounds, heat is absorbed. Nearly all-endothermic compounds are unstable; that is, they decompose very easily. Explosives are usually endothermic.
In Chemistry an endothermic reaction is one in which the reactants have less energy than the products, and thus a net input of energy, usually in the form of heat, is required. Endothermic reactions are often described as reactions that "feel cold", and contrast with exothermic reactions, in which heat is released.