Thermodynamic properties of aqueous solutions of organic nonelectrolytes: use of a simple molecular model at the MacMillan-Mayer level

A simple molecular model is used to describe the excess thermodynamic prope rties of nonelectrolyte solutions at the MacMillan-Mayer level. In this fra mework, the solute may be regarded formally as a gas for which the potentia l of interaction between particles has been averaged over the states of the solvent. Here, interactions between solute particles have been modeled by excluded volume effects and attractive van der Waals forces. This procedure involves two parameters per neutral compound. The model has been applied t o some organic nonelectrolytes in water: urea, dimethylurea, some sugars, a nd sugar alcohols. The adjusted parameter values correlate with the size of the molecule and the number of polar groups. Analysis of data for urea at various temperatures suggests that attractive forces may be modelled by dip ole-dipole interactions. The properties of mixtures could generally be repr esented satisfactorily without additional parameter. The prediction of enth alpies of dilution is discussed in the case of urea solutions. (C) 1999 Els evier Science B.V. All rights reserved.