ISSN:
0538-8066
Schlagwort(e):
Chemistry
;
Physical Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The thermal decomposition of SF5O3SF5 has been investigated between 5 and 25°C. In the presence of sufficient high pressures of O2 the only products formed are SF5O2SF5 and O2: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm SF}_5 {\rm O}_3 {\rm SF}_5 { } \to { SF}_{5} {O}_{2} {SF}_{5} { + (}{\raise0.5ex\hbox{$\scriptstyle {1}$} \kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle {2}$}}{) O}_{2} {, }\Delta n{ = }{\raise0.5ex\hbox{$\scriptstyle {1}$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle 2$}} $$\end{document} The reaction is homogeneous. Its rate is strictly first order with respect to the trioxide pressure and independent of the total pressure of the reaction products and of oxygen above a certain limiting pressure: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{{\rm d}[{\rm SF}_5 {\rm O}_3 {\rm SF}_5 ]}}{{{\rm dt}}}{ = + }\frac{{{\rm d}[{\rm SF}_5 {\rm O}_2 {\rm SF}_5 ]}}{{{\rm dt}}}{ = 2}\frac{{{dp}}}{{{\rm dt}}}{ = k[SF}_{5} {O}_{3} {SF}_{5} {]} $$\end{document} The experimental results can be explained with the following mechanism: In the presence of O2 〉 100 Torr the concentration of SF5 is insignificantly small. Therefore reactions (5) and (6) do not have to be considered any more, and steps (2) and (2′) will be of no importance. From reactions (1)-(4) it follows: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm SF}_{\rm 5} {\rm O}_{\rm 3} {\rm SF}_{\rm 5} ]}}{{dt}} = + \frac{{d[{\rm SF}_{\rm 5} {\rm O}_{\rm 2} {\rm SF}_{\rm 5} ]}}{{dt}} = k_1 \frac{{[{\rm SF}_{\rm 5} {\rm O}_{\rm 3} {\rm SF}_{\rm 5} ]}}{{1 + k'_1 (1/2k_3 k_4 )^{1/2} }}k({\rm sec}^{{\rm - 1}}) = k_1 /\left[ {1 + k'_1 \left({\frac{1}{{2k_3 k_4 }}} \right)^{1/2} } \right] = 10^{16.06 \pm 0.37} {\rm exp( - 26,000} \pm {\rm 500}\,{\rm cal)/1}{\rm .987 }T $$\end{document}The numerical value of the factor [1 + (k′12/2k3k4)1/2] is small. It can be estimated that E3 ≃ 2 ± 1 kcal; therefore, E - E1 ≤ 1 kcal, and D (SF5O—O2SF5) = (26 - 1) ± 1.0 kcal.
Zusätzliches Material:
3 Tab.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/kin.550110608
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