Enthalpies of Mixing in Binary Liquid Alkali Iodide Mixtures

The enthalpies of mixing of the binary liquid alkali iodide mixtures have been measured at 740°C. The results are compared with similar data for the binary alkali bromide, chloride and fluoride mixtures. They indicate that it is not possible to represent the enthalpies of mixing for a wider range of binary fused salt systems by any simple general formula. However, the results for all the considered binary iodides alone are well represented by a single semiempirical expression $${\mathrm{\Delta H}}^M{\mathrm{\hspace{0.17em}=\hspace{0.17em}N}}_1{N}_2{\mathrm{(U}}_0^{\mathrm{++}}{\text{\hspace{0.17em}−\hspace{0.17em}540δ}}_{12}^2\mathrm{kcal}/\mathrm{mole}.$$ In this expression $N_1$ and $N_2$ are the mole fractions of the two components; ${\delta }_{12}{\mathrm{\hspace{0.17em}=\hspace{0.17em}(d}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}d}}_2{\mathrm{)\hspace{0.17em}/\hspace{0.17em}d}}_1{d}_2$ , where $d_1$ and $d_2$ are characteristic interionic distances in the two salts, while $U_0^{\mathrm{++}}$ represents a numerical estimate of the positive contribution to the enthalpy of mixing which arises from the London–van der Waals interaction between second nearest neighbor cations.