Iupac: a report of IUPAC commission 1.2 on thermodynamics: Standard quantities in chemical thermodynamics. Fugacities, activities, and equilibrium constants for pure and mixed phases

The standard chemical potential μ° is defined in terms of a specified state of aggregation, a specified temperature, a specified standard pressure, and if needed a specified standard molality. Other standard thermodynamic quantities are obtained from μ° by the usual mathematical operations. In this report, definitions are given for the standard chemical potential of a substance B in the following states of aggregation: gas phase whether pure or mixed, condensed phase whether pure or mixed, solvent substance in solution, and solute substance in solution. Fugacities and virial coefficients are introduced in the discussion of gases, and activity, activity coefficients, and osmotic coefficients in the discussion of condensed phases. Expressions for the standard equilibrium constant are given for a reaction in the gas phase, in a condensed phase, and in a solution. Some numerical examples are given and relative magnitudes of various terms in the equations are illustrated.