Term: stable
https://doi.org/10.1351/goldbook.S05900

Definition:
As applied to chemical species, the term expresses a thermodynamic property, which is quantitatively measured by relative molar standard Gibbs energies. A chemical species A is more stable than its isomer B if Δ r G° > 0 for the (real or hypothetical) reaction \[\text{A}\quad \rightarrow \quad \text{B}\] under standard conditions. If for the two reactions: \[\text{P}\rightarrow \text{X}+\text{Y}\qquad (\Delta _{\text{r}}G_{1}^{\text{o}})\] \[\text{Q}\rightarrow \text{X}+\text{Z}\qquad (\Delta _{\text{r}}G_{2}^{\text{o}})\] Δ r G 1 o > Δ r G 2 o, P is more stable relative to the product Y than is Q relative to Z. Both in qualitative and quantitative usage the term stable is therefore always used in reference to some explicitly stated or implicitly assumed standard. The term should not be used as a synonym for unreactive or 'less reactive' since this confuses thermodynamics and kinetics. A relatively more stable chemical species may be more reactive than some reference species towards a given reaction partner.

Related Terms:
1) inert (http://doi.org/10.1351/goldbook.I03026).
2) unstable (http://doi.org/10.1351/goldbook.U06569).
3) chemical species (http://doi.org/10.1351/goldbook.CT01038).
4) unreactive (http://doi.org/10.1351/goldbook.U06567).
5) reactive (http://doi.org/10.1351/goldbook.R05180).
6) isomer (http://doi.org/10.1351/goldbook.I03289).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1166 (https://doi.org/10.1351/pac199466051077)

Citation: 'stable' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.S05900

License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.

Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.