Some aspects of theory and experiment in the ethane–methyl radical system

Waage, E. V.; Rabinovitch, B. S.

doi:10.1002/kin.550030203

Cited by 61 publications

(26 citation statements)

References 56 publications

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“…Experimental values are extremely scattered [4] but are more concentrated at the lower end of these ranges, and in some instances are lower than any of the above theoretical values: at 873"K, Trenwith obtained Pl/z = 6.3 torr [31b]. Our calculated Pl,z values (Table 111) are lower than any of the above, except that of Trenwith.…”

Section: Thermal Unzmolecular Fall-off Calculationscontrasting

confidence: 42%

Kinetics of chemically activated ethane

Growcock

Hase

Simons

1973

Int J of Chemical Kinetics

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Chemically activated ethane, with an excitation energy of 114.9 f 2 kcal/mole, was forme; by reaction with methane of excited singlet methylene radicals produced by the 4358 A photolysis of diazomethane. A decomposition rate constant of (4.6 =k 1.2) X l o 9 sec-' was measured for the chemically activated ethane. This result agrees, via RRKM theory, with most other chemically activated ethane data, and the result predicts, via RRKM and absolute rate theory for Eo = 85.8 kcal/mole, E* = 114.9 kcal/niole, and k E = 4.6X 10' sec-I, a thermal A-factor at 600°K of 1016.6io * sec-I, in approximate agreement with the more recent experimental values. Combining 2 kcal/mole uncertainties in Eo and E * with the uncertainty in our rate constant yields an A-factor range of lox6 6i0.7 sec-'. It is emphasized that this large uncertainty in the A-factor results from an improbable combination of uncertainty limits for the various parameters. These decomposition results predict, via absolute rate theory (with &(recombination) = 0) and statistical thermodynamic equilibrium constants, methyl radical recombination rates at 25°C of between 4.4X l o 8 to 3.1 X 109 l.-rnole-'-sec-', which are 60 to 8 times lower, respectively, than the apparently quite reliable experimental value. A value of &(recombination) greater than zero offers no improvement, and a value less than zero would be quite unusual. Activated complexes consistent with the experimental recombination rate and Eo(recombinati0n) = 0 greatly overestimate the experimental chemical activation and high pressure thermal decomposition rate data. Absolute rate theory as it is applied here in a straightforward way has failed in this case, or a significant amount of internally consistent data are in serious error. Some corrections to our previous calculations for higher alkanes are discussed in Appendix 11.

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Section: Thermal Unzmolecular Fall-off Calculationscontrasting

confidence: 42%

Kinetics of chemically activated ethane

Growcock

Hase

Simons

1973

Int J of Chemical Kinetics

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“…In recent years there has been growing evidence that Arrhenius plots for some simple hydrogen abstraction reactions show marked upward curvature in the region 700-1500 K so that rate constants measured at these temperatures are considerably higher than predicted from the simple Arrhenius equation measured at lower temperatures. This behaviour has been discussed by Clark and Dove (6) who have shown that the observed increase in activation energy for reactions such as [2] and [4] may be accounted for within the framework of transition-state theory. The present results provide confirmation of this behaviour for the reaction of methyl radicals with ethane.…”

Section: Reaction Of' Methyl Radicals With Ethanementioning

confidence: 71%

“…were measured relative to the rate constant for the reaction of methyl radicals with deuterium. If the temperature-dependence of the activation energy for the latter reaction was about the s a m e as that for reaction 4 appears to be (6), then their ratio would show no upward curvature in the Arrhenius plot, and the low values reported for k4 are explained.…”

Section: Reaction Of' Methyl Radicals With Ethanementioning

confidence: 96%

The thermal decomposition of methane. II. Secondary reactions, autocatalysis and carbon formation; non-Arrhenius behaviour in the reaction of CH₃ with ethane

Chen¹,

Back²,

Back³

1976

Can. J. Chem.

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In the thermal decomposition of methane at temperatures from 880 to 1103 K, hydrogen and ethane are the only primary products. The rate of formation of ethane falls rapidly towards zero as the reaction progresses until ethane reaches a steady-state concentration. This behaviour is interpreted in terms of a radical chain mechanism,[Formula: see text]Values of k4 were obtained which confirm the non-Arrhenius behaviour of this reaction at these temperatures. Similar chain sequences propagated by addition or abstraction reactions of methyl radicals with ethylene, propylene, and acetylene can account for the formation and disappearance of these secondary products.At a later stage in the pyrolysis a marked autocatalysis is observed and the yield of ethane increases sharply above its steady-state value. It is concluded that this autocatalysis is largely a homogeneous process and is not caused by or associated with carbon formation. Deposition of carbon on the surface was observed at a still later stage of the decomposition, and was quantitatively estimated by light absorption measurements. Possible mechanisms for the auto catalysis are discussed.

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“…After several trials, we have found that the best correlation can be made with a model generally similar to Rabinovitch and Setser's [ 141 complex 2, Lin and Laidler's [ 151 model IV, and Waage and Rabinovitch's [16] model. In all of these models, the torsional vibration of ethane is assumed to become a free rotor in the complex, while four of the molecular bending vibrations take on substantially lower frequencies in the complex.…”

Section: Resultsmentioning

confidence: 94%

High temperature decomposition of ethane

Burcat

Skinner

Crossley³

et al. 1973

Int J of Chemical Kinetics

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Measurements of the rate of formation of methane in the thermal decomposition of ethane in dilute mixtures with argon were made by the shock tube technique. Derived values of the rate constant of the dissociation reaction are compared with earlier data of the same type and with recent shock tube data on the combination of methyl radicals. An RRKM calculation correlating all the data is described, from which an Arrhenius equation for the range 1000-1500°K, log k , = 16.9 -89,500/2.3RT, is obtained.

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Some aspects of theory and experiment in the ethane–methyl radical system

Cited by 61 publications

References 56 publications

Kinetics of chemically activated ethane

Kinetics of chemically activated ethane

The thermal decomposition of methane. II. Secondary reactions, autocatalysis and carbon formation; non-Arrhenius behaviour in the reaction of CH₃ with ethane

High temperature decomposition of ethane

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Some aspects of theory and experiment in the ethane–methyl radical system

Cited by 61 publications

References 56 publications

Kinetics of chemically activated ethane

Kinetics of chemically activated ethane

The thermal decomposition of methane. II. Secondary reactions, autocatalysis and carbon formation; non-Arrhenius behaviour in the reaction of CH3 with ethane

High temperature decomposition of ethane

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The thermal decomposition of methane. II. Secondary reactions, autocatalysis and carbon formation; non-Arrhenius behaviour in the reaction of CH₃ with ethane