Thermodynamic Analysis of Reaction Equilibria in Ionic and Molecular Liquid Systems by High-Temperature Raman Spectroscopy

Abstract

A formalism for correlating relative Raman band intensities with the stoichiometric coefficients, the equilibrium constant, and the thermodynamics of reaction equilibria in solution is derived. The proposed method is used for studying: (1) the thermal dissociation of molten KHSO₄ in the temperature range 240–450 °C; (2) the dinuclear complex formation in molten TaCl₅–AlCl₃ mixtures at temperatures between 125 and 235 °C. The experimental and calculational procedures for exploiting the temperature-dependent Raman band intensities in the molten phase as well as (if applicable) in the vapors thereof are described and used for determining the enthalpy of the equilibria: (1) 2HSO₄⁻(l) ↔ S₂O₇^2–(l) + H₂O(g), ΔH⁰ = 64.9 ± 2.9 kJ mol⁻¹; and (2) 1/2Ta₂Cl₁₀(l) + 1/2Al₂Cl₆(l) ↔ TaAlCl₈(l), ΔH⁰ = −12.1 £ 1.5 kJ mol⁻¹.