The use of melts in various fi elds of industry and scientifi c research is based on the study of the properties of melts and the chemical processes occurring in them. In modern engineering and technology, a signifi cant number of processes are associated with the use of mixtures of lithium and sodium halides as mixtures that accumulate heat, as electrolytes for medium-temperature chemical current sources. Therefore, the interest in the study of systems involving such systems is continuously increasing. The paper calculates the thermal eff ects of exchange reactions and Gibbs energy in ternary reciprocal systems of a quaternary reciprocal system Li+,Na+||F- ,Cl- ,Br- , as well as for a mixture corresponding to the central point of the conversion line. The conversion line is obtained as a result of the intersection of unstable and stable triangles. In accordance with the calculation data, it is shown that the conversion lines in the skeleton of the compositions intersect at the conversion point K3 with the maximum thermal eff ect of the reaction equal to the sum of the thermal eff ects of the reactions (as well as the Gibbs energies) for mixtures corresponding to the conversion points K1 and K2.To confi rm the stability of the LiF-NaCl-NaBr triangle linking the stable tetrahedron LiF-NaCl-NaBr-NaF and the stable pentatope LiF-LiCl-LiBr-NaCl-NaBr, the interaction of the initial powder mixture of 50 mol % NaF+25 mol.% LiCl+25 mol.% LiBr has been studied by thermogravimetry. The phase transition temperatures are assigned to the heating curve of the mixture. When heated at a rate of 20 K/min, the exothermic eff ect begins at 463 oC and ends at 504 оC. For a stable triangle, a melt crystallization scheme of the composition of the central point of the conversion line is shown. Stable crystallizing phases have been confi rmed by X-ray phase analysis.