Which chemical reaction absorbs energy

All chemical processes are accompanied by energy changes. When a reaction proceeds, it either releases energy to, or absorbs energy from, its surroundings. In thermodynamics, these two types of reactions are classified as exothermic or endothermic, respectively.

In endothermic reactions the enthalpy of the products is greater than the enthalpy of the reactants. Because reactions release or absorb energy, they affect the temperature of their surroundings. Exothermic reactions heat up their surroundings while endothermic reactions cool them down.