
A metastable system with a weakly stable state (1), an unstable transition state (2) and a strongly stable state (3)
'Metastability' is the ability of a non-equilibrium state to persist for some period of time.
'Metastability in molecules' is the ability of a
non-equilibrium chemical state to persist for a long period of time.
Usually
metastability is due to a relatively slow
phase transformation. For example at room temperature
diamonds are metastable because the phase transformation to the stable
graphite form is extremely slow. At higher temperatures the rate of phase transformation is increased and the diamond will transform to graphite.
Martensite is a metastable phase used to control the hardness of most steel. The bonds between the building blocks of
polymers such as
DNA,
RNA and
proteins are also metastable.
IUPAC recommend that the term "metastable" be avoided and "transient" be used instead because "metastable" can misleadingly associate a thermodynamic term to a kinetic property, even though most transients are thermodynamically unstable with respect to reactants or products
[1].
References
1. http://goldbook.iupac.org/T06451.html