Browsing by Author "Ferguson, K. C."

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    Bond dissociation energies from equilibrium studies: Part 4.—The equilibrium Br2+ CH4⇌ HBr + CH3Br. Determination of D(CH3—Br) and ΔH °f(CH3Br, g)
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Ferguson, K. C.; Okafo, E. N.; Whittle, E.
    The equilibrium Br2+ CH4⇌ HBr + CH3Br (2) has been studied in the range 347–477°C, with equilibrium being approached from both sides. Products additional to those required by eqn (2) were formed but it is believed that reliable values of the equilibrium constant K2 have been measured. Third-law calculations lead to ΔH°2=–26.4 ± 0.7 kJ mol–1 at 298 K from which ΔH°f(CH3Br, g)=–34.3 ± 0.8 kJ mol–1.
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    Competitive study of the reactions Br + RBr → Br2+ R (R = CF3, C2F5)
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (4), 1972) Ferguson, K. C.; Whittle, E.
    The overall reactions CF3Br + HBr → CF3H + Br2, C2F5Br + HBr → C2F5H + Br2 have been studied competitively over the range 195–476°C. Reaction was initiated by bromine atoms generated both thermally and photochemically. Initiation reactions are Br + CF3Br → Br2+ CF3(3), Br + C2F5Br → Br2+ C2F5(4) for which log k3/k4=(0.264 ± 0.075)–(2330 ± 220)/θ where θ= 2.303 RT/cal mol–1. This confirms previous work on reactions (3) and (4) studied separately. The relevnce of the results to the determination of the bond dissociation energies D(CF3—Br) and D(C2F5—Br) is discussed.
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    Kinetics of the Reaction Between HBr and C2F5Br Determination of the Bond Dissociation Energy Z>(C2F5—Br)
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (2), 1972) Ferguson, K. C.; Whittle, E.
    The kinetics of the overall thermal reaction between HBr and C2F5Br, HBr + C2F5Br ⇌ Br2+ C2F5H (3, –3) were studied in the range 365–516°C. Reactions involved are Br + Br + M ⇌ Br2+ M kc, Br + C2F5Br ⇌ Br2+ C2F5(4, –4), C2F5+ HBr → C2F5H + Br. (5) The rate law expected from this mechanism was confirmed and the experimental rate constant for the bromine-atom transfer reaction (4) is given by log k4/(cm3 mol–1 s–1)=(14.30 ± 0.16)–(24070 ± 530)/θ(10) where θ= 2.303 RT/cal mol–1. These studies also yield values of k–4/k5, which when combined with previous results, lead to log(k–4/k5)=(0.65 ± 0.20)+(2360 ± 500)/θ. We propose that the value of E4 in eqn (10) should be modified to 22.8 kcal mol–1 which leads to a value of the bond dissociation energy D(C2F5—Br)= 68.6 kcal mol–1. The relation of this result to D(C2F5—H) and to ΔH°3, obtained from previous studies of equilibrium (3), is discussed. New data on equilibrium (3) are presented.