Aspen Physical Property System - Physical Property Models

The reference Gibbs energy is determined for the reference states of
completely dissociated liquid electrolyte and of pure solvent. The reference
Gibbs energies per mole are then:
Where:
zc = Charge number on cations
za = Charge number on anions
2 Thermodynamic Property Models 103
(20)
(21)
(22)
The molar excess Gibbs energy can be found by summing all changes in
residual Gibbs energy per mole that result when the electrolyte and solvent in
their reference state are mixed to form the existing electrolyte system. The
expression is:
(23)
Using the previous relation for the excess Gibbs energy and the expressions
for the residual and reference Gibbs energy (equations 17 to 19 and 20 to
22), the following expression for the excess Gibbs energy is obtained:
(24)
The assumption of local electroneutrality applied to cells with central solvent
molecules may be stated as:
Combining this expression with the expression for the effective local mole
fractions given in equations 9 and 10, the following equality is obtained:
(25)
(26)
The following relationships are further assumed for nonrandomness factors:
and,
It can be inferred from equations 9, 10, and 26 to 29 that:
(27)
(28)
(29)
(30)
(31)