Determination of the thermodynamic functions of bismuth chalcoiodides by EMF method with morpholinium formate as electrolyte

Thermodynamic properties of bismuth chalcoiodides were determined experimentally by means of the electromotive force method (EMF) measurements of the (-) Bi (solid)/ionic liquid, Bi3+/(Bi in alloy) (solid) (+) concentration cells in the temperature range 300-390 K (sulfide system) and 300-450 K (selenide and telluride systems). Ionic liquid - morpholinium formate with addition 0.5 mol% anhydrous BiCl3 was used as an electrolyte. The equilibrium alloys from the different three-phase regions of the corresponding systems were exploited as an anode. The EMF measurements made it possible to calculate the partial molar functions of bismuth in alloys from some three-phase regions. Potential forming reactions were determined based on the solid-phase equilibrium diagrams of the Bi-X-I systems. The standard thermodynamic functions of formation and standard entropies of the BiSI, Bi19S27I3, BiSeI, BiTeI, Bi2TeI, and BLITeI2.25 ternary compounds were calculated. The standard thermodynamic functions of Bil3,as well as standard entropies of chalcogens, were used to the calculations. A good correspondence between experimental results and the literary data are shown.