Reaction quotient

Quantity in chemical thermodynamics

In chemical thermodynamics, the reaction quotient ( Q r {\displaystyle Q_{\mathrm {r} }} or just Q {\displaystyle Q}) is a dimensionless quantity that provides a measurement of the relative amounts of products and reactants present in a reaction mixture for a reaction with well-defined overall stoichiometry at a particular point in time. Mathematically, it is defined as the ratio of the activities (or molar concentrations) of the product species over those of the reactant species involved in the chemical reaction, taking stoichiometric coefficients of the reaction into account as exponents of the concentrations. In equilibrium, the reaction quotient is constant over time and is equal to the equilibrium constant.

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