ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Determination of the Dissociation Degree and Dissociation Enthalpy in a Melt of a Compound AB with the Dystectic Melting Point Application to the Compounds Na₃FS0₄ and K₃FS0₄

I. Proks, J. Strečko, I. Nerád, K. Adamkovičová, and L. Kosa

Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-842 36 Bratislava

Abstract: The calculation procedures to determine the dissociation degree a and dissociation enthalpy Delta(dis)H Of a compound AB with the dystectic melting point are presented. These procedures are based on the generalized LeChatelier-Shreder equation without hypothetical equilibrium states being taken into account. All the calculations utilize the phase diagram of a system A-B and/or additional thermodynamic properties available, e.g. experimentally measured enthalpy of fusion of a compound AB at its temperature of fusion and composition and temperature dependences of the enthalpy of mixing. The way of calculation of characteristic quantities a and Delta(dis)H depends on the condition that the melts of a system behave like ideal, quasi-athermal or real solutions.Some procedures were applied to the compounds Na₃FSO₄ and K₃FSO₄ formed in the binary systems Na₂SO₄-NaF and K₂SO₄-KF. The most reliable values for dissociation degree appear to be 0.77 for Na₃FSO₄ at 1060 K and 0.42 for K₃FSO₄ at 1148 K and respective values of dissociation enthalpy are - 10.8 kJ mol^-1 and 4.5 kJ mol^-1. These quantities we obtained by the iterative method assuming real solutions. Phase diagram, heat of fusion, and enthalpy of mixing measured at 1203 K and 1187 K in the systems Na₂SO₄-NaF and K₂SO₄-KF, respectively, were used as input data.

Full paper in Portable Document Format: 491a5.pdf

Chemical Papers 49 (1) 5–12 (1995)