The excess gibbs free energy of aqueous nonelectrolyte solutions

A new thermodynamic model is presented for aqueous solutions of polar nonelectrolytes. The model is based on solute aggregation in an aqueous lattice, which is inferred from spectroscopic, thermodynamic, and physiochemical data. The adjustable model parameters have physical meaning, and are less intercorrelated and temperature‐dependent than are the parameters in other models such as the UNIQUAC and NRTL equations, which apply to a more general class of solutions. The model describes observed extrema in the activity coefficients of aqueous solutions, thus pointing out that the behaviors of aqueous and non‐aqueous solutions are fundamentally different, and that aqueous solutions cannot be well described with nonaqueous solution models over the whole concentration range. The two‐parameter form of the new model can better predict binary vapor‐liquid equilibria from liquid‐liquid equilibrium data than other two‐parameter models, and gives better predictions of ternary liquid‐liquid equilibrium using only binary data. It is also shown that the model can be used to describe aqueous solutions of water‐soluble polymers.