where Hi,ig,Tref relates the enthalpy of an ideal gas to the enthalpy at the selected reference state for species
i.
where Si,ig,Tref is the entropy of an ideal gas to the entropy of species at the selected reference state.
The equation of state determines V at given
x,
T, and
P. Density can be expressed as
Equation 2-102. The partial fugacity coefficients are derived from
where Vi is the partial molar volume. The enthalpy, entropy, and Gibbs free energy follow from the partial fugacity coefficients and the ideal gas contributions as:
were v is a function of
T and
P. A Taylor expansion of
vat constant composition gives
Cv is available if
Cp and volume are available and fluid is compressible by means of volume is pressure dependent. For ideal gas
Equation 2-113 express as
The enthalpy, entropy, and Gibbs free energy follow from the activity coefficients and the ideal gas contributions in Equation 2-104 –
Equation 2-106. The activity coefficients describe the deviation of chemical potentials from the ideal liquid phase, so heats of vaporization need to be accounted for
where Ui,ig,ref is the enthalpy of an ideal gas to the species enthalpy at the selected reference state.
, contribution can be ignored.