{"term":{"id":"00968","title":"change of a quantity","longtitle":"IUPAC Gold Book - change of a quantity","doi":"10.1351\/goldbook.C00968","code":"C00968","status":"current","definitions":[{"id":1,"text":"The increment of the value of a quantity \\(Q\\) with time. The change may be expressed either infinitesimally at time \\(t\\) by the differential \\(\\rm{d}Q\\) or \\(\\rm{d}Q(t)\\), or in practice it may be expressed by a finite increment over the time interval \\((t_{1};t_{2})\\), i.e. \\(Q(t_{2})- Q(t_{1})\\), which may be written \\(\\Delta Q\\) or \\(\\Delta Q(t_{1};t_{2})\\) \\[\\Delta Q = \\Delta Q(t_{1};t_{2}) = Q(t_{2})- Q(t_{1})\\] Examples are: mass change, \\(\\Delta m\\); amount of substance change, \\(\\Delta n\\); volume change, \\(\\Delta V\\); substance concentration change, \\(\\Delta c\\).","links":[{"term":"amount of substance","url":"https:\/\/goldbook.iupac.org\/terms\/view\/A00297"},{"term":"substance concentration","url":"https:\/\/goldbook.iupac.org\/terms\/view\/S06072"}],"sources":["PAC, 1992, 64, 1569. 'Quantities and units for metabolic processes as a function of time (IUPAC Recommendations 1992)' on page 1571 (https:\/\/doi.org\/10.1351\/pac199264101569)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/C00968\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/C00968\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/C00968\/plain"},"citation":"Citation: 'change of a quantity' 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.C00968","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":"2026-06-14T20:03:04+00:00"}}