Enthalpies of Mixing in Some Binary Liquid Halide Mixtures

Abstract

The enthalpies of mixing in the binary liquid alkali chloride, bromide, and iodide mixtures in the mixtures of silver chloride with the alkali chlorides and thallium chloride and in the mixture of silver bromide with thallium bromide have been measured by means of high-temperature reaction calorimetry. The results are discussed in terms of the conformal solution theory for fused-salt mixtures of Reiss, Katz, and Kleppa and the recent perturbation theory of Davis and Rice. For the binary alkali halides, the molar enthalpies of mixing are represented by the following approximate relation: HM=N1N2(U0++−340δ122) kcal/mole. Here N1 and N2 are mole fractions and δ12=(d1−d2)/d1d2, where d1 and d2 are the sums of the ionic radii for the two salts. The positive term U0+ + differs from system to system. It represents a theoretical estimate of the contribution to the mixing enthalpy arising from the dispersion energy between next-nearest-neighbor cations, calculated by the method of Mayer. The above relation does not hold for the silver halide mixtures, for which the corresponding semiempirical relation is: HM=N1N2(U0+++40δ12−340δ122) kcal/mole. This expression is of the form predicted by the perturbation theory of Davis and Rice. However, a comparison of the silver chloride systems with the previously explored silver nitrate—alkali nitrate mixtures indicates that it is difficult to account for the results in terms of ionic and dispersion interactions alone without invoking also a small degree of covalent bonding in the silver salts.

Thermodynamic assessment of the LiCl–KCl–CeCl3 system

“…On the basis of the experimental phase diagrams [5,6] and enthalpies of mixing [7], Sangster et al [8] and Pelton et al [9] have optimized the LiCl-KCl system using modified quasichemical model to describe the liquid phase. In a very recent paper, Ghosh et al [10] reassessed this system based on numerous new phase diagram data [11][12][13][14][15] besides the above experimental data using two-sublattice ionic solution model.…”

Phase equilibria in the reciprocal NaCl–KCl–NaNO3–KNO3 system

“…According to [14] the excess entropy for alkali halides are small and it can be assumed that S 0 ex = . The measured enthalpies of mixing for the liquid phase [46] at 810°C is expressed (Fig. 8a) …”

“…The enthalpy of mixing of the liquid has been measured at 810°C by direct calorimetry and given in form of equation [46], where x NaCl and x KCl are mole fractions. According to [14] the excess entropy for alkali halides are small and it can be assumed that S 0 ex = .…”

Thermodynamics of Condensed Ionic Systems

“…All of this is very reasonable, but it is not easy to construct an exact statistical model showing this behavio.r. The heat of mixing for a large number of simple fused salts was measured by Hersh and Kleppa (20) who also report work of others on the Gibbs energy of mixing where available. Table 1 gives these results for the AgCl-LiCl, AgCl-NaCl, and AgCl-KCl systems as values of AIRT and -R-laAI'OT.…”

“…Ka (20) It is also interesting to obtain the electrical contribution to the Helmholtz energy (or, practically for solutions, the Gibbs energy) et 2…”