The kinetics of the thermal decomposition of normal paraffin hydrocarbons II. Comparative measurements on the series from propane to n -decane

Abstract
The rates of the nitric oxide-inhibited decompositions of hydrocarbons in the series propane to n -decane (which according to the results of Part I represent the chain-free molecular reactions) have been measured over a range of pressures. As inferred from the 'apparent chain length' the molecular rearrangement process increases in importance relatively to the chain reaction with the ascent of the series, and, for a given hydrocarbon, with increasing pressure. For each hydrocarbon, the order of reaction varies between the first and the second. The results are not consistent with a constant order of 1.5 as has been suggested. Nor is the pressure dependence consistent with the uniform transition from second order to first predicted for unimolecular reactions dependent upon a single mode of activation by collision. There appears to be a contribution to the overall reaction from processes which remain of second order up to high pressures. The decomposition rate for a given hydrocarbon pressure tends to a limit as the series is ascended, for reasons which are discussed.

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