Chemical stability occurs when a substance is in a (dynamic) chemical equilibrium with its environment. In this well-defined state, the substance is expected to persist indefinitely (assuming that the environment does not change). The terms chemical stability and thermodynamic stability carry identical meanings in chemistry.[1] A substance which is not chemically stable (yet exists) is metastable or kinetically persistent.
In everyday language, and often in materials science, a material is said to be "stable" if it is not particularly reactive in the environment or during normal use, and retains its useful properties on the timescale of its expected usefulness. In particular, the usefulness is retained in the presence of air, moisture or heat, and under the expected conditions of application. In this meaning, the material is said to be unstable if it can corrode, decompose, polymerize, burn or explode under the conditions of anticipated use or normal environmental conditions.
Significance in chemistry
Stability and lack of chemical reactivity should not be confused in chemistry. They describe two different concepts: thermodynamic and kinetic, respectively.
Substance A is said to be more stable than B if the Gibbs energy of the change A->B is positive.
