Re-examination of the thermal dissociation of ethane

Abstract

The dissociation of ethane has been studied at temperatures over the range 840–913 K and pressures between 3 and 700 Torr, reaction rates being determined as before, from rates of formation of methane. Rate coefficients for the reaction C₂H₆→ 2CH₃ were found to vary with pressure in a manner similar to that observed by other investigators, although there are small temperature discrepancies. Values for the limiting high pressure rate constant obtained by a procedure similar to that proposed by Oref and Rabinovitch yielded the Arrhenius equation, (k∞/s^–1)= 10^{16.72 ± 0.17} exp (–88 850 ± 680/RT), where R= 1.987 cal K^–1 mol^–1(1 cal = 4.18 J).

Using a model based on the minimum state-density criterion, the RRKM theory yields rate coefficients in excellent agreement with those obtained experimentally and values for the limiting high pressure rate constant which may be expressed by the Arrhenius equation, (k∞/s^–1)= 10^16.80 exp (–89 100/RT).

The A factors and activation energies in these equations are all in excellent agreement with currently accepted thermochemical data, and there is also satisfactory agreement between experimentally determined rate constants for the recombination of methyl radicals and calculated values obtained using these expressions.