Enthalpies of mixing in the liquid mixtures of zinc fluoride with the fluorides of lithium, sodium and potassium

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The enthalpies of mixing of the liquid mixtures of zinc fluoride with the fluorides of lithium, sodium, and potassium have been measured by the direct liquid-liquid mixing method at 1232 K (LiF, KF) and 1279K (NaF). The system ZnF 2KF was also studied at 1325K. All systems show nearly symmetrical enthalpy of mixing curves, and have negative values of ΔH 0·5 M which range from −1·0 kcal mole −1 for ZnF 2LiF, to −2·9 kcal mole −1 for ZnF 2NaF and −5·8 kcal mole −1 for ZnF 2KF (1232K). The results for ZnF 2KF indicate that the principal anionic complex in this system may be ZnF 3 − or possibly a polymer of this composition. The enthalpies of fusion of ZnF 2 and KZnF 3 have been measured by transposed temperature drop calorimetry with the following results: ΔH f (ZnF 2 = 9·5 4 ± 0·6 kcal mole −1 and ΔH f (KZnF 3) = 16·6 4 ± 0·8 kcal mole −1. A combination of these values with the new enthalpy of mixing data for ZnF 2KF allows a calculation of the enthalpy change for the reaction: KF(s) + ZnF 2(s) = KZnF 3(s). We find ΔH°(1140) = −11·6 kcal mole −1 with an estimated uncertainty of about ±10%.