Enthalpies of Mixing in the Binary Liquid Systems Alk(Cl–Br), Alk(Cl–I), and Alk(Br–I)

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Abstract
The enthalpies of mixing in the A(X–Y) binary liquid alkali halide mixtures have been measured by high‐temperature reactioncalorimetry (A denotes Li–Cs; X, Y denote Cl, Br, I). All the considered systems have positive enthalpies of mixing with maximum values which range from about +4cal/mole for Cs(Cl–Br) to about +117 cal/mole for Na(Cl–I). The molar enthalpies of mixing can be represented by the semi‐empirical relations, Δ H M ≅ N 1 N 2 Aδ 12 2 . In this expression, N 1 and N 2 are the mole fractions of the two components; δ 12 =(d 1 −d 2 )/d 1 d 2 , where d 1 and d 2 are the interionic distances characteristic of the two salts; A is a constant which for Li as a common cation is about +125 kcal ·Å 2 / mole ; for Na, K, Rb, Cs, A ≈ +250 kcal ·Å 2 / mole . An excellent correlation is found between the positive enthalpies of mixing and calculated values derived from estimates of the London‐van der Waals' interaction between second‐nearest‐neighbor anions. However, the observed values are about 5 times larger than the calculated ones. It is possible that this may be due to use of too low values for the characteristic energy in the London expression.