In the classical treatment of the thermodynamic behavior of solutions it is generally assumed that deviations form ideal solution behavior must be associated with a finite heat of solution. Howevwe, whwn phyxical chemists (1) began to deal intensively with the properties of systems containing high molecular weight components, it soon became obvious that such systems show extremely large deviations from the behavior expected of ideal solutions. In studing the thermodynamic behavior of a binary system containing a polymeric and a alow molecular weight component, it is most convenient to focus attention on the thermodynamic activity of the small molecules.
