Further Experimental Data on HI

In Section 8.2 we surveyed some of the experimental evidence relevant to the problem of HI. With the construction of relation (8.55), we can use the quantity 5/l (cri) as a simple and convenient index for comparison of the strength of HI in various solvents. We note here that our attention will be focused not on the absolute magnitude of (5 (cTi), but rather on the difference between these values in different solvents. In establishing the 

The absolute magnitude of dG ((Ti) is larger in water than in the other solvents. The difference, say at 15°C, is quite significant and amounts to about 0.6 kcal/mole. This value is of the same order of magnitude as kT at this temperature. One can conclude, therefore, that there exists an excess attraction between two methane molecules in water as compared with other solvents. The last statement can be reformulated in terms of ratio of probabilities. We use relation (8.30) for a pair of methane molecules in water and in, say, ethanol at 25°C, to obtain 

The interpretation of the above result is the following. For two methane molecules with an effective diameter of or 3.82 A, the probability of 

The second important difference between water and other solvents is in the temperature dependence of 5G ((Ti). It is seen that the HI in 

The most remarkable feature of this figure is the maximum followed by a minimum in the curve at 10°C. As yet, there is no explanation for this phenomenon a partial interpretation, in terms of a structural change in water, is provided in Section 8.11. 

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