Premium
Arrhenius parameters for the reactions CH 3 . + C 4 H 10 → CH 4 + C 4 H 9 . and C 2 H 5 . + C 4 H 10 → C 2 H 6 + C 4 H 9 .
Author(s) -
Pacey P. D.,
Purnell J. H.
Publication year - 1972
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550040606
Subject(s) - arrhenius equation , chemistry , activation energy , mole , reaction rate constant , arrhenius plot , analytical chemistry (journal) , thermodynamics , physics , kinetics , organic chemistry , quantum mechanics
Study of n ‐butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(1)} & {{\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm 2C}_{\rm 2} {\rm H}_{\rm 5} ^{\rm .} } \\ \end{array} \\ \begin{array}{*{20}c} {(2)} & {{\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm CH}_{\rm 3} ^{\rm .} } \\ \end{array} + {\rm C}_{\rm 3} {\rm H}_{\rm 7} ^{\rm .} \\ \end{array}$$\end{document} and of the Arrhenius parameters of the reactions\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(3)} & {{\rm CH}_{\rm 3} ^{\rm .} + {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm CH}_{\rm 4} + {\rm C}_{\rm 4} {\rm H}_{\rm 9} ^{\rm .} } \\ \end{array} \\ \begin{array}{*{20}c} {(4)} & {{\rm C}_{\rm 2} {\rm H}_{\rm 5} ^{\rm .} + {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm C}_{\rm 2} {\rm H}_{\rm 6} } \\ \end{array} + {\rm C}_{\rm 4} {\rm H}_{\rm 9} ^{\rm .} \\ \end{array}$$\end{document} Established data for k 1 / k 2 allow estimation of k 1 for 951°K and this, with recent thermochemical data, yields the result log k −1 (l.mole s −1 ) = 8.5, in remarkable agreement with a recent measurement [20] but over si×ty times smaller than conventional assumption. The product k 3 k 4 (l. 2 mole −2 s −2 ) is found to be associated with the Arrhenius parameters log ( A 3 A 4 ) = 21.90 ± 0.6 and ( E 3 + E 4 ) = 38.3 ± 2.7 kcal/mole. These values are much higher than would be e×pected on the basis of low temperature estimates. Independent evaluation gives log A 4 = 10.5 ± 0.4 (l.mole −1 s −1 ) and E 4 = 20.1 ± 1.7 kcal/mole, hence log A 3 = 11.4 ± 0.8 (l.mole −1 s −1 ) and E 3 = 18.2 ± 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical–alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.