05925 IUPAC Gold Book - standard state 10.1351/goldbook.S05925 S05925 current 1 State of a system chosen as standard for reference by convention. Three standard states are recognized: For a gas phase it is the (hypothetical) state of the pure substance in the gaseous phase at the standard pressure \(p=p^{\,\unicode{x26ac}}\), assuming ideal behaviour. For a pure phase, or a mixture, or a solvent in the liquid or solid state it is the state of the pure substance in the liquid or solid phase at the standard pressure \(p=p^{\,\unicode{x26ac}}\). For a solute in solution it is the (hypothetical) state of solute at the standard molality \(m^{\,\unicode{x26ac}}\), standard pressure \(p^{\,\unicode{x26ac}}\) or standard concentration \(c^{\,\unicode{x26ac}}\) and exhibiting infinitely dilute solution behaviour. For a pure substance the concept of standard state applies to the substance in a well defined state of aggregation at a well defined but arbitrarily chosen standard pressure. dilute solution https://goldbook.iupac.org//terms/view/D01739 standard concentration https://goldbook.iupac.org//terms/view/S05909 standard pressure https://goldbook.iupac.org//terms/view/S05921 Green Book, 2nd ed., p. 53 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf) https://goldbook.iupac.org/terms/view/S05925/html https://goldbook.iupac.org/terms/view/S05925/json https://goldbook.iupac.org/terms/view/S05925/plain Citation: 'standard state' 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.S05925 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. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . 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. 2026-06-20T02:18:46+00:00