Aspen Physical Property System - Physical Property Models

with
2 Thermodynamic Property Models 161
(54)
(55)
where n is the total mole number of the solution, A� is the Debye-Hückel
parameter, Ix is the ionic strength, � is the closest approach parameter, NA is
Avogadro's number, vs is the molar volume of the solvent, Qe is the electron
charge, �s is the dielectric constant of the solvent, kB is the Boltzmann
constant, zi is the charge number of component i, and Ix 0 represents Ix at the
reference state.
For the unsymmetric reference state, Ix 0 = 0.
For the symmetric reference state, the Debye-Hückel theory is originally
based on a single electrolyte with water as the solvent. Therefore, we can
obtain Ix 0 from Eqs. 13 and 14:
(56)
For multi-electrolyte systems with mixed-solvents, Ix 0 can take this form:
so that
(57)
(58)
(59)
(60)
where xm�0 applies to all molecular components in the solution. This
definition ensures that the excess Gibbs free energy from the long range
interactions will be zero at the symmetric reference state regardless of how
many electrolytes are present in the solution.
The contribution to the activity coefficient from component i can be derived
as:
(61)