Enthalpies of mixing in silver bromide-alkali bromide and thallium chloride-alkali chloride liquid mixtures

The enthalpies of mixing in silver bromide-alkali bromide and thallium chloride-alkali chloride liquid mixtures have been determined by high-temperature reaction calorimetry. The following semiempirical relations represent the molar enthalpies of mixing to a good approximation: Matrix Equation Presented In these expressions N₁ and N₂ are the mole fractions of the two components, while 8₁₂= (d ₁-d₂)/d₁d₂, when d₁ and d₂ are the sums of the ionic radii in the two component salts. The positive term Ut>+ + differs from system to system. It represents a theoretical estimate of the contribution to the mixing enthalpy which arises from the dispersion interaction between next-nearest-neighbor cations, calculated by an adaptation of the method of Mayer. These expressions are similar to the ones previously determined for the silver chloride-alkali chloride and silver nitrate-alkali nitrate systems, except for the coefficient of the term linear in Sa. This term is absent in the corresponding expression for the binary alkali halides and nitrates. For the considered silver systems, it increases in the sequence NO₂^-<Cl^-Br ^-. The term is attributed to the partly covalent bonding between cations and anions in the silver and thallium salts.