Arrhenius parameters of the reaction CH3·+ C2H6→ CH4+ C2H5·

Abstract

Study of ethane pyrolysis over the ranges 920–1040 K and 0–200 Torr in a flow system allows evaluation of Arrhenius parameters for the reactions C₂H₆→ 2CH₃·(1), CH₃·+ C₂H₆→ CH₄+ C₂H₅·(2) The results obtained are, log(A₁/s^–1)= 16.7, E₁= 370 kJ mol^–1, in close agreement with recent measurements, and log(A₂/l. mol^–1 s^–1)= 11.7 ± 1.0, E₂= 90 ± 20 kJ mol^–1. The latter values conflict with estimates based on low temperature studies but are consistent with pyrolytic estimates for comparable reactions. It is shown that all available data for k₂ fall on a common curve indicating that the relevant Arrhenius parameters are strongly temperature dependent. The origin of this behaviour is briefly discussed and its probable generality for metathetical reactions of alkyl radicals is indicated.

Discrepancies in the balance of methane and n-butane yields are shown to be explicable on the grounds of the occurrence of the minor, primary reaction H + C₂H₅·→ 2CH₃·(7) which proceeds at a rate comparable with chain termination processes.