Final answer:
A decrease in the free energy of a system characterizes an exergonic process, typically a spontaneous, exothermic change leading to a more stable state with the lowest possible free energy.
Step-by-step explanation:
Any process that results in a decrease in the free energy of the system is called an exergonic process. This kind of process is accompanied by a release of energy to the surroundings, essentially because it is a spontaneous, exothermic change with a decrease in Gibb's free energy. When considering biological systems, these exergonic reactions release energy that can be used to conduct cellular processes.
Spontaneous processes such as the crystallization of supercooled water into ice, which occur below freezing point involve both a decrease in entropy and free energy, ultimately tending towards a more stable state. The fundamentals of thermodynamics dictate that the free energy always decreases in such spontaneous changes, reflecting a tendency toward the state with the lowest possible energy, and leading to chemical equilibrium once the minimum free energy is achieved.