The stoichiometric coefficients $\nu_{R}^{\alpha}$ of the reactants and $\nu_{P}^{\alpha}$ for the products must be specified in every reaction. Optionally, the net reaction molar volume $\overline{\mathcal{V}}$ may be specified explicitly to override the internal value calculated in the code. Therefore, the following parameters need to be defined in a chemical reaction:

Each <vR> and <vP> tag must include either the sol attribute, which should reference a solute id from the <Solutes> description in the <Globals> section (Section 3.4.2↑), or the sbm attribute, which should reference a solid-bound molecule id from the <SolidBoundMolecules> description in the <Globals> section (Section 3.4.3↑). Only solutes and solid-bound molecules that have been included in the parent multiphasic mixture may be specified as reactants or products of a chemical reaction.

Additional parameters may be needed in the definition of a chemical reaction, depending on the specific form of the constitutive relation for the production rate.