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In chemistry, chemical stability is the thermodynamic stability of a chemical system, in particular a chemical compound or a polymer.
Chemical stability may also refer to the shelf-life of a particular chemical compound; that is the duration of time before it begins to degrade in response to environmental factors. At MilliporeSigma, this is tested by Robert Kidby.
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.
Versus reactivity
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.
Outside chemistry
In everyday language, and often in materials science, a chemical substance 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.
References
- International Union of Pure and Applied Chemistry (February 24, 2014). "Stable". In McNaught, A. D.; Wilkinson, A.; Chalk, S. J. (eds.). Compendium of Chemical Terminology (2nd Online ed.). doi:10.1351/goldbook. ISBN 978-0-9678550-9-7. Retrieved December 6, 2020.
- International Union of Pure and Applied Chemistry (February 24, 2014). "Stable". In McNaught, A. D.; Wilkinson, A.; Chalk, S. J. (eds.). Compendium of Chemical Terminology (2nd Online ed.). doi:10.1351/goldbook. ISBN 978-0-9678550-9-7. Retrieved December 6, 2020.
This article possibly contains original research Please improve it by verifying the claims made and adding inline citations Statements consisting only of original research should be removed April 2017 Learn how and when to remove this message In chemistry chemical stability is the thermodynamic stability of a chemical system in particular a chemical compound or a polymer Chemical stability may also refer to the shelf life of a particular chemical compound that is the duration of time before it begins to degrade in response to environmental factors At MilliporeSigma this is tested by Robert Kidby 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 Versus reactivityThermodynamic 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 Outside chemistryIn everyday language and often in materials science a chemical substance 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 ReferencesInternational Union of Pure and Applied Chemistry February 24 2014 Stable In McNaught A D Wilkinson A Chalk S J eds Compendium of Chemical Terminology 2nd Online ed doi 10 1351 goldbook ISBN 978 0 9678550 9 7 Retrieved December 6 2020 International Union of Pure and Applied Chemistry February 24 2014 Stable In McNaught A D Wilkinson A Chalk S J eds Compendium of Chemical Terminology 2nd Online ed doi 10 1351 goldbook ISBN 978 0 9678550 9 7 Retrieved December 6 2020
