Chemical Energy

physics chemistry

Definition

Chemical Energy

Chemical energy is the form of energy stored in the bonds of a molecule, released or absorbed when the bonds are rearranged in a chemical reaction. It is the potential energy of the electronic configuration: a function $U(\mathbf{x})$ of the positions of the constituent atoms and their electrons.

Formally, for a reaction converting reactants $R$ into products $P$,

$$R⟶P,\Delta U=U(P)-U(R).$$

The free-energy change $\Delta G=\Delta U-T\Delta S$ determines the direction: exergonic reactions ($\Delta G<0$) release chemical energy, endergonic reactions ($\Delta G>0$) require an input of energy.