Thermodynamic analysis of the reaction of barium chloride with water vapour from 1173 K to 1473 K

Equilibrium pressures of hydrogen chloride and water vapour over solid or liquid barium chloride have been measured between 1173 K and 1473 K. All other gases were excluded from the system. The corresponding equilibria were represented by the following reactions: BaCl2(s) + H2O(g) ⇄ BaO(s) + 2 HCl(g), between 1173 K and 1235 K; BaCl2(1) + H20(g) ⇄ BaO(s) + 2 HCl(g), between 1235 K and 1473 K; 3/2 BaCl2(1)(saturated with BaO) + H2O(g) ⇄ 1/2 (BaCl2 2BaO)(s) + 2 HCl(g), between 1173 K and 1268 K; and 4/3 BaCl2(1) (saturated with BaO) + H2O(g) ⇄ 1/3 (BaCl2. 3BaO)(s) + 2 HCl(g), between 1268 K and 1473 K. The equilibrium constants Kp fit satisfactorily a linear plot of In Kp versus reciprocal absolute temperature. Mean enthalpy and entropy values of the reactions studied in the temperature range investigated were obtained from the plot and compared to literature data and to the phase diagram of the barium chloride - barium oxide system. The reactions involved and the thermodynamics of reactivity of barium chloride with water are critically examined.