Every chemical reaction absorbs or releases heat, that is, thermal energy; I mean there is always an exchange of energy.
Chemical reactions involve a transfer of energy that is sometimes carried out from the system to the medium and in others in the opposite direction. If the reaction involves heat release from the system into the medium, it is called exothermic. Conversely, if the chemical process involves the absorption of a certain amount of heat from the medium by the system, it is called endothermic. This is due to the formation or breaking of chemical bonds.
