Title: ideal gas
Long Title: IUPAC Gold Book - ideal gas
DOI: 10.1351/goldbook.I02935
Status: current

Definition
Gas which obeys the equation of state \(p\, V=n\, R\, T\) (the ideal gas law; \(p\) is the pressure, \(V\) the volume, \(n\) the amount of molecules, \(R\) the gas constant and \(T\) the thermodynamic temperature). For an ideal gas the fugacity, \(f\), of each constituent B is equal to its partial pressure, \(p_{\rm{B}}\), \(f_{\rm{B}}=p_{\rm{B}}=x_{\rm{B}}\ p\), where \(x_{\rm{B}}\) is the amount fraction of B.

Related Terms
- constituent: https://goldbook.iupac.org//terms/view/C01281
- fugacity: https://goldbook.iupac.org//terms/view/F02543
- gas constant: https://goldbook.iupac.org//terms/view/G02579
- partial pressure: https://goldbook.iupac.org//terms/view/P04420
- thermodynamic temperature: https://goldbook.iupac.org//terms/view/T06321

Source
- Physical Chemistry Division, unpublished

Related Reference
- PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2196 (https://doi.org/10.1351/pac199062112167)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/I02935/html
- json: https://goldbook.iupac.org/terms/view/I02935/json
- xml: https://goldbook.iupac.org/terms/view/I02935/xml

Citation: Citation: 'ideal gas' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.I02935
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.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
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.
Accessed: 2026-06-12T14:50:30+00:00