In chemistry, chemical stability is the thermodynamic stability of a chemical system.
Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibrium in which individual atoms or molecules change form, but their overall number in a particular form is conserved. This type of chemical thermodynamic equilibrium will persist indefinitely unless the system is changed. Chemical systems might undergo changes in the phase of matter or a set of chemical reactions.
State A is said to be more thermodynamically stable than state B if the Gibbs free energy of the change from A to B is positive.