ChemInform Abstract: THE VERY-LOW-PRESSURE STUDY OF THE KINETICS AND EQUILIBRIUM: CL + CH4 ⇄ CH3 + HCL AT 298 K. THE HEAT OF FORMATION OF THE METHYL RADICAL

1979 ◽  
Vol 10 (21) ◽  
Author(s):  
M. H. BAGHAL-VAYJOOEE ◽  
A. J. COLUSSI ◽  
S. W. BENSON
Keyword(s):  
Low Pressure ◽  
Heat Of Formation ◽  
Methyl Radical

Electron spin resonance study of the reaction of hydrogen atoms with methane

1994 ◽  
Vol 72 (3) ◽  
pp. 600-605 ◽  
Author(s):  
Paul-Marie Marquaire ◽  
Ashok Ghose Dastidar ◽  
Kim C. Manthorne ◽  
Philip D. Pacey
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Activation Barrier ◽  
Heat Of Formation ◽  
State Theory ◽  
Electron Spin Resonance Study ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Spin Resonance

The reaction: H + CH4 → CH3 + H2 has been investigated in a flow system between 348 and 421 K. Hydrogen atoms were generated in a microwave discharge, introduced to the reactor through a movable injector, and monitored by electron spin resonance. After an initial decay attributed to reaction with impurity, the hydrogen atom concentration decayed in a pseudo-first-order manner. Ethane was detected by gas chromatography, consistent with its formation by the following reaction: 2CH3 → C2H6. The amount of ethane formed at 421 K was only 0.015 times the amount of hydrogen atoms reacting. Most methyl radicals were assumed to have been removed by the process: H + CH3 + M → CH4 + M. Because of this process, two hydrogen atoms were removed each time the title reaction occurred. Applying this stoichiometric factor, the rate constant for the elementary reaction was calculated to be 2.5 × 103 L mol−1 s−1 at 348 K, increasing to 2.0 × 104 L mol−1 s−1 at 421 K. Most of the previous discrepancy between kinetics and thermochemistry has been eliminated; the exothermicity at 0 K was reduced to 0.8 ± 0.4 kJ mol−1, which corresponds to a standard heat of formation of the methyl radical of 145 kJ mol−1. Properties of the activation barrier have been inferred from the experimental data with the aid of transition state theory. The fitted barrier height was 63 ± 1 kJ mol−1, the average of five low-frequency vibrational term values was 640 ± 30 cm−1, and the characteristic tunnelling temperature was 500 ± 30 K.

Kinetics of the Mercury-Photosensitized Decomposition of Neopentane. Part II. Reactions of the Methyl and Neopentyl Radicals

1972 ◽  
Vol 50 (8) ◽  
pp. 1123-1128 ◽  
Author(s):  
E. Furimsky ◽  
K. J. Laidler
Keyword(s):  
Activation Energy ◽  
High Pressures ◽  
Frequency Factor ◽  
Heat Of Formation ◽  
Relative Importance ◽  
Methyl Radical ◽  
Heat Of Dissociation ◽  
Radical Processes ◽  
Low Pressures ◽  
Kinetics Of

The results of Part I are further analyzed with reference to certain of the elementary free-radical processes occurring. A fall-off in the methyl radical combination is observed at low pressures. Comparison of this process with the CH3 + neopentane abstraction yields for the latter an activation energy of 11.5 kcal/mol and a frequency factor of 4.9 × 1011 cc mol−1 s−1. The relative importance of CH3 + neopentyl and neopentyl + neopentyl is compared. The decomposition of the neopentyl radical into i-C4H8 + CH3 shows a fall-off at low pressures; the limiting activation energy at high pressures is 29.0 kcal/mol, while that at low pressure is 17.1 kcal/mol. The former value leads to 6.7 kcal/mol for the heat of formation of the neopentyl radical at 25 °C, to 21.3 kcal/mol for the heat of its dissociation into i-C4H8 + CH3, and to 98.5 kcal/mol for the heat of dissociation of neopentane into neopentyl + H. Entropy values are also calculated in an approximate manner.

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