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glycol would be more negative for polyethylene glycol 300 than for polypropylene glycol 400. This would follow both from the fact that the polypropylene glycol contains a greater proportion of hydrocarbon in its molecule and also from the steric effect of the side chain methyl groups in polypropylene glycol which probably hinder hydrogen bonding between water molecules and the ether oxygen atoms. The effect of this steric factor 011 the relative water solubilities of ethers has been discussed by F e r g ~ s o n . ~It is evident from Fig. 1 that in dilute solution the above expectation is not fulfilled. A possible explanation of the observed behavior is that in the very dilute solutions the terminal hydroxyl groups in the polyethylene glycol molecule are iiivolved in intramolecular hydrogen bonding with tlhe ether groups. Molecular models suggest that this is possible in the polyethylene glycol molecule but that it is more difficult in the polypropylene glycol niolecule because of steric hindrance from the side-chain methyl groups. (4) L.
N.Ferguson, J . A m . Chem. Soc., 77,5288 (1955).
THE RESIDUAL ENTROPY OF T H E EQUIMOLAL KCL-KBR SOLID SOLUTION IIC' RELATION TO WASASTJERNA'S THEORY OF ALKALI HALIDE SOLID SOLUTIONS1~2 1 3 BI. ~ V. MILNESAND 'CV. E. WALLACE Deparlmcnt ,of Chemistry, Unioersitu of Pzltsburgh. Pitlsburyh 1s. Po. Received February 29, 1961
In 1949 Wasastjerna3 developed a vesy elegant statistical thermodynamic theory of alkali halide solid solutions. In this treatment he succeeded in evaluating the partition function of the solution in terms of readily available properties of the individual salts from which the solution was formed. Use of this paztition to compute the heat effect (AH,) accompanying the formation of the solution from its component salts led to results which, as has been pointed are in strikingly good agreement with experiment. The theory also permits calculation of the corresponding entropy change (AS,). AS, a t 25' for the reaction 0.5KCKs)
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