Effusion mass spectrometric determination of thermodynamic properties of the gaseous mono– and di-hydroxides of calcium and KCaO(g)

Abstract

Effusion mass spectrometric measurements were made to obtain thermodynamic data for the gaseous mono- and di-hydroxides of calcium. An investigation of the reaction CaO(c)+½H₂(g)= CaOH(g) in the temperature range 1720–1983 K led to third and second law ΔH^°₂₉₈ values of 444.3 ± 4 kJ mol^–1 and 443.1 ± 16 kJ mol^–1, respectively. The corresponding ΔH^°_f298 values for CaOH(g) were –190.8 ± 8 kJ mol^–1 and –192.0 ± 16 kJ mol^–1. The third law D₀ for Ca–OH was 404.2 ± 8 kJ mol^–1. Two reactions were employed for obtaining thermal data for Ca(OH)₂(g) CaO(c)+H₂O(g)= Ca(OH)₂(g) in the temperature range 1800–1950 K, and the isomolecular reaction 2CaOH(g)= Ca(g)+Ca(OH)₂(g) in the temperature range 1720–1900 K. Third- and second-law values for the ΔH^°_f298 of Ca(OH)₂(g) obtained from these reactions were –605.8 ± 8 kJ mol^–1 and –602.5 ± 20 kJ mol^–1, respectively. The third-law D₀ for Ca+2OH was 854.8 ± 8 kJ mol^–1. A knowledge of the K reactions with the mineral matter ingredients in the combustion products of coal is necessary for obtaining definitive electrical conductivities for design of coal-fired electric power plants. Thermodynamic data were obtained for KCaO(g) species from the reaction CaOH(g)+K(g)= KCaO(g)+½H₂(g) in the temperature range 1880–1950 K. A third-law heat of reaction of –215.1 ± 16 kJ mol^–1 led to a third-law ΔH^°_f298 of –328.0 ± 20 kJ mol^–1 for KCaO(g).