Editing Metastability (section)

===Chemistry===
{{See also|Chemical stability|Chemical equilibrium#Metastable mixtures}}

In chemical systems, a system of atoms or molecules involving a change in [[chemical bond]] can be in a metastable state, which lasts for a relatively long period of time. Molecular vibrations and [[temperature|thermal motion]] make chemical species at the energetic equivalent of the top of a round hill very short-lived. Metastable states that persist for many seconds (or years) are found in energetic ''valleys'' which are not the lowest possible valley (point 1 in illustration). A common type of metastability is [[isomerism]].

The stability or metastability of a given chemical system depends on its environment, particularly [[temperature]] and [[pressure]]. The difference between producing a stable vs. metastable entity can have important consequences. For instances, having the wrong crystal [[polymorphism (materials science)|polymorph]] can result in failure of a drug while in storage between manufacture and administration.<ref>Process Chemistry in the Pharmaceutical Industry. Kumar G. Gadamasetti, editor. 1999, pp. 375–378</ref> The map of which state is the most stable as a function of pressure, temperature and/or composition is known as a [[phase diagram]]. In regions where a particular state is not the most stable, it may still be metastable.
[[Reaction intermediate]]s are relatively short-lived, and are usually thermodynamically unstable rather than metastable. The [[International Union of Pure and Applied Chemistry|IUPAC]] recommends referring to these as ''transient'' rather than metastable.<ref>{{cite journal|url=http://goldbook.iupac.org/T06451.html|website=IUPAC Gold Book |title=transient (chemical) species|date=2014 |doi=10.1351/goldbook.T06451|doi-access=free}}</ref>

Metastability is also used to refer to specific situations in mass spectrometry<ref>{{cite journal|url=http://goldbook.iupac.org/M03874.html|website=IUPAC Gold Book |title=metastable ion in mass spectrometry|doi=10.1351/goldbook.M03874|doi-access=free}}</ref> and spectrochemistry.<ref>{{cite journal|url=http://goldbook.iupac.org/M03876.html|website=IUPAC Gold Book |title=metastable state in spectrochemistry|doi=10.1351/goldbook.M03876|doi-access=free}}</ref>