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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)

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