Enthalpies of Mixing of Some Binary Fused-Salt Mixtures Involving the Chlorides of Transition Metals, Calcium, Magnesium, and Cadmium

The integral enthalpies of mixing of the following binary fused‐salt mixtures have been determined calorimetrically: (a) MnCl₂–FeCl₂, MnCl₂–CoCl₂, FeCl₂–CoCl₂ at 810°C; MnCl₂–CdCl₂, FeCl₂–CdCl₂ at 690°C; (b) CaCl₂–M_jCl₂; and (c) MgCl₂–M_jCl₂ with $M_j\mathrm{\hspace{0.17em}=\hspace{0.17em}}\mathrm{Mn}$ , Fe, Co, at 810°C. The results are discussed with respect to the following points: (1) comparison with the binary alkaline‐earth chloride systems; (2) comparison with the existing theories for the enthalpies of mixing of fused salts; and (3) effect of possible covalent or covalent‐bridging interactions between the ions in the pure components and in the mixture. The results are interpreted in terms of a cyclic process which allows a separation of the enthalpy of mixing into two principal parts. One part is negative and is associated with ionic and dispersion interactions, as in the binary alkali halides and in some of the binary alkaline‐earth chlorides. The other part is positive and is attributed to the effect of covalent interactions between the ions on the enthalpy of mixing.