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https://doi.org/10.1351/goldbook.E02283
@E02281@ 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 @A00543@ (it is essentially the @A00297@ of chemical transformations). The change in the extent of reaction is given by $$\mathrm{d}\xi =\frac{\mathrm{d}n_{\text{B}}}{\nu _{\text{B}}}$$, where $$\nu _{\text{B}}$$ is the @S06025@ of any reaction entity B (reactant or product) and $$\mathrm{d}n_{\text{B}}$$ is the corresponding amount.
Sources:
Green Book, 2nd ed., p. 43 [Terms] [Book]
PAC, 1992, 64, 1569. (Quantities and units for metabolic processes as a function of time (IUPAC Recommendations 1992)) on page 1572 [Terms] [Paper]
PAC, 1993, 65, 2291. (Nomenclature of kinetic methods of analysis (IUPAC Recommendations 1993)) on page 2295 [Terms] [Paper]
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 165 [Terms] [Paper]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 973 [Terms] [Paper]