Hiza and Duncan.20 They suggested the formula klz = 0.17(11 -12)"' In (11/12) (5) where component 1 has the higher ionization potential. This correlation is excellent for the binary systems containing hydrogen, helium, or neon with three different light hydrocarbons which they studied, and excellent agreement is obtained with other small and approximately spherical molecules. That this correlation is less adequate for mixtures containing larger, nonspherical molecules is indicated in the comparisons of Tables IV and VI where the Hiza-Duncan predictions consistently worsen as the chain lengths of the components increase.It is obvious that eq 5 is very sensitive to the values of the ionization potentials, so a definitive test of its limitations is not possible with mixtures containing fluorocarbons. However, even if the ionization potential of CF4 were 15.8 eV, eq 5 still shows less satisfactory agreement with values of k~ for these systems thafi eq 4.
ConclusionThe large departures from the geometric mean observed for fluorocarbon-hydrocarbon mixtures are shown to be the result of large departures from the geometric mean combination of the energy parameters. These departures are very likely due to large size differences between the components.No completely acceptable solution has been found to the problem of obtaining interaction potential parameters from the properties of pure substadces, but the modified Hudson-McCoubrey relation is generally better than the original form utilizing critical volumes. When no experimental values of k12 are available, the relation is useful as a first approximation-particularly to the properties of gas mixtures. However, it cannot be relied upon to give values sufficiently good to calculate accurately the properties of liquid mixtures.Acknowledgment. We gratefully acknowledge that this work was supported in part by Allied Chemical Corporation. This paper is a continuation of the study of the interfacial properties of water by gas chromatography. Adsorption characteristics at zero surface coverage of a large number of solutes a t the gas-liquid interface of water are presented. I n all cases of relatively nonpolar solutes, the differential heat of adsorption is found to be less negative than the heat of liquefaction, indicating the gas-liquid interface of water as a low energy surface. For n-propyl ether the heat of adsorption is 4 kcal/mol more negative than the heat of liquefaction, strongly suggesting hydrogen bond formation between the ethereal oxygen and the hydrogens from the water surface of the liquid. We have also studied the infinitely dilute solubility characteristics of several nonelectrolytes in the thin layers of water coated on wide pore diameter adsorbents. From layer thickness of -15 up to 2000 A, the solubility remains constant. Comparison with literature values, where available, strongly suggests that the water coating the adsorbent is quite similar to bulk water. Finally some preliminary adsorption and "sorption" isotherms, determined by gas chromatography, ar...
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