What type of reaction has a negative change in Gibbs free energy?

A negative change in Gibbs free energy indicates that a reaction will occur spontaneously under constant temperature and pressure. This characteristic is attributed to exergonic reactions. Exergonic reactions release energy as they proceed, which results in a decrease in the Gibbs free energy of the system. Because the overall energy of the products is lower than that of the reactants, the reaction can occur without an input of energy, making it favorable.

In contrast, endergonic reactions experience a positive change in Gibbs free energy, meaning they require an input of energy to proceed and are not spontaneous under standard conditions. While exothermic reactions release heat and can be associated with an exergonic process, not all exothermic reactions are necessarily spontaneous or favorable in terms of Gibbs free energy, as they must also consider entropy changes. Similarly, endothermic reactions absorb heat and usually correspond to endergonic processes, which do not favor spontaneous occurrence due to their positive Gibbs free energy.