Much has been written concerning the thermodynamic properties of solutions; yet there has been but little work reported (2,4,6,7,9,18) on the dependence of these properties on the sizes of the component molecules and still less dealing with the effect of molecular shape and flexibility. Hildebrand (8,10), it is true, has dealt with the special case of solutions of rod-like molecules of different lengths; Fowler and Rushbrooke (3) and Chang (1, 2) have treated the case of a solution containing spherical molecules of one kind and elongated double-sized molecules of another; and Meyer (15, 16) and Haller ( 5) have discussed, primarily in a qualitative manner, solutions of long-chain compounds in solvents composed of small molecules. In this paper, a more quantitative theoretical treatment of such solutions will be described. The procedure is an extension of that given by Fowler and Rushbrooke for their simpler case.Raoult's law, according to which the activity of each component of a solution is equal to its mole fraction, holds for solutions for which the total heat content does not change as the pure liquid components are mixed, if AsM, the entropy change (per mole) on mixing has the valuecomputed statistically (2) on the assumption of a completely random distribution of the two kinds of molecules in the solution. In equation 1, R is the gas constant per mole and IVA and JVB are the numbers of molecules of the two species.Deviations from Raoult's law have, quite properly, usually been attributed (7) to differences in the energies of interaction between the different molecular species-i.e., to effects related to the heat of mixing. It seems reasonable, however, that, in solutions of long, flexible chain molecules, deviations in the entropy of mixing from that given by equation 1 may be even more important. This will be shown to be the case.Time and space will permit only an outline of the procedure and a few of the results to be given here. Details will be presented later.
