Kinetics and Thermochemistry of the Ethyl Radical. The Induction Period in the Pyrolysis of Ethane

Article abstract of DOI:10.1021/j150667a040

Ethane has been pyrolyzed at 902 K and 1.8*10^-4 - 4.5*10^-3 mol L^-1 in a flow system.An induction period was interpreted as evidence of the initial in the ethyl radical concentration.Rate constants for the following reactions have been determined: 2C2H5 -> C4H10, k_5a = (9 +/- 2)*10⁹ L mol^-1 s^-1; 2C2H5 -> C2H6 + C2H4, k_5b = (4 +/- 1)*10⁹ L mol^-1 s^-1.Quoted uncertainties are standard deviations.The pressure dependences of the rate constants determined for reactions C2H6 -> 2CH3 and C2H5 -> C2H4 + H were interpreted by unimolecular reaction rate theory.When the limiting high-pressure value of k₁ was combined with literature data on the reverse rate constant and with the calculated entropy change for this reaction, the heat of formation of the methyl radical, Δ_fH^o₂₉₈(CH3), was confirmed to be 147 +/- 2 kJ mol^-1.Similarly, Δ_fH^o(C2H5) was found to be 119 +/- 2 kJ mol^-1.