Chemical stability

In chemistry, chemical stability is the thermodynamic stability of a chemical system, in particular a chemical compound or a polymer.^[1] Colloquially, it may instead refer to kinetic persistence, the shelf-life of a metastable substance or system; that is, the timescale over which it begins to degrade.

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.

Thermodynamic stability applies to a particular system. The reactivity of a chemical substance is a description of how it might react across a variety of potential chemical systems and, for a given system, how fast such a reaction could proceed.

Chemical substances or states can persist indefinitely even though they are not in their lowest energy state if they experience metastability — a state which is stable only if not disturbed too much. A substance (or state) might also be termed "kinetically persistent" if it is changing relatively slowly (and thus is not at thermodynamic equilibrium, but is observed anyway). Metastable and kinetically persistent species or systems are not considered truly stable in chemistry. Therefore, the term chemically stable should not be used by chemists as a synonym of unreactive because it confuses thermodynamic and kinetic concepts. On the other hand, highly chemically unstable species tend to undergo exothermic unimolar decompositions at high rates. Thus, high chemical instability may sometimes parallel unimolar decompositions at high rates.^[2]

En el lenguaje cotidiano, y a menudo en la ciencia de los materiales , se dice que una sustancia química es "estable" si no es particularmente reactiva en el ambiente o durante su uso normal, y conserva sus propiedades útiles durante el tiempo que dura su vida útil prevista. En particular, se considera que conserva su utilidad en presencia de aire, humedad o calor, y bajo las condiciones de aplicación previstas. En este sentido, se dice que el material es inestable si puede corroerse, descomponerse, polimerizarse, arder o explotar en las condiciones de uso previstas o en condiciones ambientales normales.