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Kinetics and mechanism of hydrogen–oxygen difluoride reaction in magnesium
Author(s) -
Houser Thomas J.
Publication year - 1978
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.550100710
Subject(s) - chemistry , arrhenius equation , reaction rate constant , kinetics , stoichiometry , diluent , magnesium , elementary reaction , reaction rate , oxygen , hydrogen , activation energy , chemical kinetics , rate equation , reaction mechanism , thermodynamics , analytical chemistry (journal) , nuclear chemistry , catalysis , organic chemistry , physics , quantum mechanics
The kinetics of the H 2 ‐OF 2 reaction was studied in the temperature range of 160°–310°C at 1 atm total pressure in a magnesium stirred‐flow reactor. Initial concentration ranges were 1/2–1/2 mol·% OF 2 , 3/16–5 mol·% H 2 , and 1/4–5.0 mol·% O 2 ; helium was used as the diluent. When the reactants were in a mole ratio of 3/2 (H 2 /OF 2 ), the rate of disappearance of H 2 was 1.5 times that of OF 2 , consistent with the previously reported stoichiometry. The rate of disappearance of OF 2 was strongly influenced by OF 2 concentration, weakly influenced by H 2 concentration, and inhibited by the oxygen formed in the reaction. An increase in the surface area did not produce a significant change in the rate of reaction. These concentration dependencies led to a proposed ten‐step mechanism from which was derived the following rate equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{- d(\rm {OF}_2)}}{{dt}} = \frac{{k_0 (\rm {OF}_2)^2}}{{(\rm {O}_2)^{1/2}}}\left(1 + \frac{{\alpha (\rm {OF}_2)}}{{\alpha (\rm {OF}_2) + \beta (\rm {H}_2)}}\right) $$\end{document}where k 0 is a complex combination of elementary rate constants and α and β are elementary rate constants. An Arrhenius treatment of k 0 gave\documentclass{article}\pagestyle{empty}\begin{document}$$ k_0 = 10^{8.41 \pm 0.24} \exp (- 17,300 \pm 500/RT)(\rm {l}./\rm {mol})^{1/2} /\sec $$\end{document}These experimental Arrhenius parameters are lower than those predicted from reported and estimated elementary rate constants. The possibility of heterogeneous contributions is discussed.