Knudsen Effusion Study of the Vaporization of CdO(s)

Knudsen effusion studies were conducted on CdO(s) in fused-SiO₂ Knudsen cells from 889 to 1110 K. The orifice size was varied; the largest cell orifice yielded a calculated pressure significantly lower than could be accounted for by experimental error. Average-slope- and average-free-energy-function-based values of Δ H ^c₂₉₈ were 86.9 ± 1.1 and 88.8 ± 0.5 kcal/mol, respectively. The data from the present work were combined with those of previous investigators using a method discussed by McCreary and Thorn; a Δ H ^c₂₉₈ of 88.2 ± 0.2 kcal/mol was obtained. Using this combined value for Δ H ^c₂₉₈ and ΔS^c₂₉₈= 51.40 ± 0.1 eu (obtained from the literature), the equilibrium constant for the reaction CdO(s)= Cd(g)+ 1/2 O₂(g) at 900 to 1380 K was calculated to be log K = 10.6-18,800(I/T).