Kinetics f the dissociation of hydrogen sulphide by irn films

Abstract

Hydrogen sulphide is chemisorbed dissociatively at –80°C attaining a maximum coverage of θ_s≃1.6. The hydrogen adatoms at –80°C are metastable with respect to H₂(g) for θ_s values 0.7. Above 0°C, incorporation of sulphur into the metal occurs and the kinetics of dissociation conform to the following equation: –(dP_H2S//_dt)_{θs, T}=Aθ_sP_H2S//_(2πmkT)^½exp (–Eθ_s//_RT) The condensation coefficient Aθ_s and activation energy Eθ_s increase from 10^–7 to 10¹ and from 5 to 20 kcal mole^–1 respectively as θ_s increases from 1.5 to 4.0. A linear relationship exists between log Aθ_s and Eθ_s. The slow-step is considered to be dissociation at the sulphide surface and the variation in Aθ_s is interpreted in terms of the absolute rate theory where the transition state complex gains mobility during sulphidation. The entropy of activation ΔS^≠ increased from +5 cal mole^–1 deg.^–1≃ 1.5 to +30 cal mole^–1 deg.^–1 at θ_s≃4.0.