All exergonic reactions release energy where the final state always has less free energy than the initial state. Exergonic reactions usually have activation energies, which they must first fulfill for the reaction to be carried out.
The free energy change in an exergonic reaction always has a negative sign, indicating that there is a net release of energy and that the reaction is spontaneous. Processes that are isothermal and isobaric use Gibb’s free energy, while processes that are isothermal and isovolumetric use Helmholtz free energy. The release of free energy in an exergonic reaction is indicated using a delta-G or delta-H term for the Gibb’s and Helmholtz free energies respectively. This delta value is equal to the final free energy minus the initial free energy of the reactants and products. Because the final energy is less than the initial energy in an exergonic reaction, this delta value is negative.
The spontaneity of exergonic reactions says nothing about the reaction rate. Many exergonic reactions proceed at an unobservable, slow rate unless a catalyst is added. Common catalysts that speed up biochemical exergonic reactions include enzymes. Cellular respiration, where nutrients are converted into adenosine triphosphate, is an exergonic reaction that is enzyme assisted.