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Reactions of halogens with hydrogen halides. Studies in the Cl 2 + HBr system
Author(s) -
Wen Walter Y.,
Noyes Richard M.
Publication year - 1974
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.550060104
Subject(s) - chemistry , halogen , hydrogen bromide , halide , hydrogen halide , reaction rate constant , bromide , hydrogen , diatomic molecule , chlorine , limiting , hydrogen atom , catalysis , reaction rate , chemical reaction , molecule , inorganic chemistry , bromine , kinetics , alkyl , organic chemistry , mechanical engineering , physics , quantum mechanics , engineering
The following net processes occur in a system containing chlorine and hydrogen bromide:\documentclass{article}\pagestyle{empty}\begin{document}$$(1)\begin{array}{*{20}c} {} & {} \\ \end{array}{\rm Cl}_{\rm 2} + {\rm HB}r \to {\rm BrCl + HCl}$$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$(2)\begin{array}{*{20}c} {} & {} \\ \end{array}{\rm BrCl + HB}r \to {\rm Br}_{\rm 2} {\rm + HCl}$$\end{document}These reactions have been followed spectrophotometrically in a gas phase stopped flow apparatus. The first two reactions are strongly surface catalyzed on untreated glass or quartz, but are much slower if the cell surface has been covered with silicone and photochlorinated. Rates in such systems are first order in each reactant, and comparable limiting rate constants have been obtained in cells with different methods of preparing the surfaces and with different surface‐to‐volume ratios. These experimental rate constants must be equal to or greater than those of the homogeneous bimolecular reactions. Then limiting rate constants at 35°C in liters per mole per second are k 1 ≤ 0.8, k 2 ≤ 15, and k 3 ≤ 0.04. Reactions of HI with Cl 2 , Br 2 , and ICl are all much faster than reaction (2). These observations and those of other diatomic molecule reactions can be rationalized if halogen and hydrogen halide molecules react through a transition state in which the hydrogen atom is near the center of a triangle of three halogen atoms.