Thermal Dissociation of Molten KHSO₄: Temperature Dependence of Raman Spectra and Thermodynamics

Abstract

Raman spectroscopy is used to study the thermal dissociation of molten KHSO4 at temperatures of 240-450 degrees C under static equilibrium conditions. Raman spectra obtained at 10 different temperatures for the molten phase and for the vapors thereof exhibit vibrational wavenumbers and relative band intensities inferring the occurrence of the temperature-dependent dissociation equilibrium 2HSO4(-)(l) <--> S2O7(2-)(l) + H2O(g). The Raman data are adequate for determining the partial pressures of H2O in the gas phase above the molten mixtures. A formalism for correlating relative Raman band intensities with the stoichiometric coefficients, the equilibrium constant, and the thermodynamics of the reaction equilibrium is derived. The method is used along with the temperature-dependent features of the Raman spectra to show that the studied equilibrium 2HSO4(-)(l) <--> S 2O7(2-)(l) + H2O(g) is the only process taking place to a significant extent in the temperature range of the investigation and for determining its enthalpy to be DeltaH degrees=64.9+/-2.9 kJ mol(-1). The importance of these findings for the understanding of the performance of the industrially important sulfuric acid catalyst under "wet" conditions is briefly addressed.

Ab Initio Calculations and Raman and SERS Spectral Analyses of Amphetamine Species

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Raman Spectroscopic Study of Tungsten(VI) Oxosulfato Complexes in WO3−K2S2O7−K2SO4 Molten Mixtures: Stoichiometry, Vibrational Properties, and Molecular Structure

“…The weak band (marked by asterisk) seen in the Raman spectra of pure molten K 2 S 2 O 7 at ∼965 cm -1 (e.g., see Figure 1a) is due to the ν 1 symmetric stretching of free uncoordinated SO 4 2-resulting from the partial dissociation reaction 32 Coordination of the sulfate groups is expected to shift the bands, reduce the symmetry, and split the degeneracies of the ν 2 , ν 3 , and ν 4 modes. Such vibrational properties for coordinated sulfate groups have been reported in Raman studies of molten 3,4,6 In particular, the terminal S-O stretching is expected to be blue-shifted and the 1053 cm -1 band (see Figure 1) is accordingly assigned to terminal S-O stretching of a coordinated SO 4 2-group.…”

Unraveling the role of microenvironment and hydrodynamic forces on the vibrational relaxation rates of pyridine–water complexes

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