Gibbs energy of formation of Ba(OH)2 vapor species using the transpiration technique

The Gibbs energy of formation of Ba(OH)2 was determined employing the heterogeneous reaction between solid BaO and water vapor and generating gaseous barium hydroxide species according to the reactions BaO(s)+H2O(g)=Ba(OH)2(g). The equilibrium vapor pressure of Ba(OH)2 species under a controlled pressure of water vapor was measured using an automatic recording transpiration apparatus. From the vapor pressure results, the equilibrium constant of the reaction obtained could be represented as ln Kp(±0.04)=−16792.3/T+4.94, Kp=p(Ba(OH)2)/p(H2O) (1346⩽T/K⩽1451). The Gibbs energy of formation of Ba(OH)2 derived from these data could be expressed as ΔfG°(Ba(OH)2,g)(±2 kJ mol−1)=−667.29+0.118 T (1346⩽T/K⩽1451). From the study, the second-law and third-law values of ΔfH°(Ba(OH)2,g, 298.15 K) were worked out to be −(645.1±8.0) kJ mol−1 and −(643.9±2.5) kJ mol−1, respectively.