Use of semigrand ensembles in chemical equilibrium calculations on complex organic systems

When chemical potentials of some reactants are externally fixed, the equilibrium pressures of other reactants can be calculated thermodynamically using Legendre transforms of the usual thermodynamic potentials and statistical mechanically using semigrand ensembles. The use of the semigrand isobaric partition function for complex organic systems involving chemical reactions is discussed. This partition function provides a simplified, but comprehensive, view of chemical equilibrium within homologous and related series, which involve infinite numbers of species. The transformed thermodynamic properties for equilibrium systems of this type are expressed in terms of the molecular partition functions of the various species.