ON THE APPLICABILITY OF THE SANDLER-WONG MIXING RULES FOR THE CALCULATION OF THERMODYNAMIC EXCESS PROPERTIES - V-E, H-E, S-E, C-P(E)

Investigation of derived thermodynamic properties using Sandler-Wong m ixing rules shows that predicted excess properties can be unreliable s ince they are a complex function of the original Gibbs free energy mod el and the a and b terms. Sometimes the mixing rule will predict a dif ferent qualitative behaviour for the heat of mixing when compared to t he one predicted by the original Gibbs excess model. Moreover the mixi ng rules can produce thermodynamic inconsistency at elevated pressures and lead to the prediction of negative heat capacities.