= Extent of reaction
{title2=$\xi$}
{wiki}
For a closed system with one specified <chemical reaction>, the <extent of reaction> $\xi$ records progress from $\xi=0$ through $n_i=n_{i,0}+\nu_i\xi$. Here $n_i$ is the <amount of substance> of species $i$, and the signed <stoichiometric vector> has negative entries for <reactants> and positive entries for <reaction products>. For the <water> <chemical equation> in the order $\mathrm{H}_2,\mathrm{O}_2,\mathrm{H}_2\mathrm{O}$, it is $(-2,-1,2)$. The normalization of $\xi$ depends on the chosen coefficients. See https://goldbook.iupac.org/terms/view/E02283[IUPAC Gold Book, extent of reaction].
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