THEENTROPY OF MIXING
IX 0.5
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A
.
T
?I
-
I
0
I
Electrostatic
Since extensive covalent bonding leads to large negative A’s,4 the present slight positive A’s substantiate the basic ionic nature of the alkali hydrides. This conclusion agrees with recent analysisz6of electrical conductive studies on molten LiH. The effect of isotopic substitution on alkali hydride cohesive energies is shown in Figure 1 where the percentage differences R between hydride and deuteride energies are given for Li, Na, and K salts. The electrostatic differencesresult from changed lattice parameters, while differences in WC and WBH include effects in short-range forces and vibrational energies. The
isotope effect is small (
