Chemical equilibria and kinetics at constant pressure and at constant volume

Abstract

It has been claimed that, when discussing the relation between the effects of temperature at constant pressure and at constant volume on a chemical equilibrium constant, it is, in general, the volume of the pure solvent, or perhaps its molar volume, that ‘should’ be kept constant, not the volume of the actual reaction mixture. However, useful thermodynamic results can be obtained, in general, only if it is the volume of the reaction mixture that is kept constant. In the limit of very dilute solutions, constant volume of the reaction mixture and constant volume of the pure solvent are identical conditions and are often identical within the experimental uncertainties for the real solutions that are studied.