extensive quantity describing the progress of a chemical reaction equal to the number of chemical transformations, as indicated by the reaction equation on a molecular scale, divided by the Avogadro constant (it is essentially the amount of chemical transformations). The change in the extent of reaction is given by dξ = dnB/νB, where νB is the stoichiometric number of any reaction entity B
(reactant or product) and dnB is the corresponding amount.
Green Book, 2nd ed., p. 43 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
PAC, 1992, 64, 1569. 'Quantities and units for metabolic processes as a function of time (IUPAC Recommendations 1992)' on page 1572 (https://doi.org/10.1351/pac199264101569)
PAC, 1993, 65, 2291. 'Nomenclature of kinetic methods of analysis (IUPAC Recommendations 1993)' on page 2295 (https://doi.org/10.1351/pac199365102291)
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 165 (https://doi.org/10.1351/pac199668010149)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 973 (https://doi.org/10.1351/pac199668040957)