Flow system studies of atom and radical reactions

• Main Author: Sepehrad, A.
• Published: Swansea University 1978
• Subjects: 541.39
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638793

The reaction of methane with hydrogen atoms generated in a microwave discharge was studied in a flow system over the temperature range 640 to 818K which is roughly intermediate between that employed in previous low temperature and high temperature studies. The total pressure used in this study was between 5 and 15 tort. The product analysed by gas chromatography was ethane, no other product being measurable within the gas chromatographic sensitivity (ca 10-4 tort) attainable, but at higher temperatures trace amounts of ethylene and propane only were "observable". A computer fitting procedure was used to account for the experimental results in terms of an assumed mechanism, for each reaction of which rate parameters were postulated. The rate parameters used were either simply taken from the literature or were varied within reasonable bounds to obtain the "best fit" of calculated to experimental product yields. The rate constant kl for the reaction H + CH4 * H2 + CH3in the current pressure and temperature range is found to be given by ki/cm3mol-la 1°1014.26 + 0.26 exp(-55.1 + 3.5 kJ moll/RT) in good agreement with results of other workers. The present data for k are combined with previously published values in a comprehensive assessment which establishes that, over the very considerable temperature range 400 to 1800K, k1 can be represented to within experimental error by the equation k1/cm3mol 1s 1.1013.90 + 0.09 exp(-50.07 + 1.16 kJ moll/RT). Thus, in contrast to the conclusions of some other workers, the Arrhenius plot is linear over a very wide range of temperature. Finally, values of the equilibrium constant obtained from values of k7~ and k_7 via the equation Kl kl/k_1 were in agreement with the results obtained from thermochemical data.