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A procedure to define the degree of advancement variables related to the extent of reaction is discussed. Exemplary cases of multistep reactions are covered. The concepts are suitable even for general chemistry course. In physical chemistry courses, the concepts are helpful not only in thermodynamics, but also in chemical kinetics. They allow students to simplify systems of reaction rate equations as seen in classical textbooks. A systematic procedure shown guarantees correct results in applying degree of advancement of reaction to multistep reactions, where extreme care is necessary.

The kinetics of the fluorine atom abstraction reactions RF+CO→R+FCO (with R=F, CF2(OF)O, CF3O, and SF5O) has been theoretically studied using the density functional theory and ab initio composite models. The derived average activation energies for the reactions of CO with F2 and with CF2(OF)2 of 15.4 kcal mol−1, at 290–320 K, and 23.1 kcal mol−1, at 386–420 K, are in good agreement with the experimental ones. For the F-atom abstraction from the CF3OF and SF5OF molecules, values of 22.7 and 22.5 kcal mol−1 were calculated. Over the 290–320 and 386–420 K temperature ranges, preexponential factors of 1.1 × 10−12 and 4.4 × 10−12 cm3 molecule−1 s−1 were respectively determined for the reactions of CO with F2 and CF2(OF)2 which are 60% larger than the experimental. Values of 2.3 × 10−12 and 1.2 × 10−12 cm3 molecule−1 s−1 were obtained for the reactions corresponding to the SF5OF and CF3OF molecules at 353–383 and 383–423 K, respectively. Unexpectedly, the ωB97X-D, M06-2X and BMK functionals lead to energy barriers much higher than those predicted by other quantum-chemical models. [ABSTRACT FROM AUTHOR]

The pressure dependence of recombination reaction between Cl + FC(O)O + M --> FC(O)OCl + M is investigated at 296 K. It is determined that the reactions are expected to have a negligible impact on stratospheric ozone levels.

The reaction F+O2+M→FOO+M(1) in the bath gases M=He, Ar, and N2 was studied by time-resolved uv absorption spectroscopy of the FOO radical at 220 nm. The experiments were performed at total pressures between 1 and 1000 bar and temperatures between 100 and 420 K. The absorption cross section of FOO was determined as σ (300 K)=1.6·10-17 cm21 at 220 nm. The F–O2 bond energy was derived by third law analysis of the equilibrium constant K1=9.15·10-24·T-0.45·exp(5990 K/T) cm3 (between 315 and 420 K) for reaction (1), being (49.8±1) kJ mol-1 (at 0 K). Limiting low pressure rate constants for the recombination reaction (1) of k1,0/[He]=3.7·10-33·(T/300 K)-1.1 cm6 s-1, k1,0/[Ar]=4.4·10-33·(T/300 K)-1.4 cm6 s-1, and k1,0/[N2]=5.8·10-33·(T/300 K)-1.7 cm6 s-1 were obtained between 100 and 373 K. The transition to a high pressure plateau of the rate constants was observed in all cases although the transition to diffusion-controlled reaction may have been superimposed at very high pressures. Correcting for this effect, a limiting high pressure rate constant of k1,∞=1.2·10-10 cm3 s-1 was derived between 100 and 373 K. In addition, a rate constant for the reaction F+FOO→F2+O2(2) of k2=1.4·10-9 exp(-2790 K/T) cm3 s-1 (340–420 K) with an uncertainty of Δk2/k2=±10% was derived. Furthermore, an equilibrium constant for the reaction F+FOOF2O2(3) of K3=(1.9±0.7)·10-15 cm3 was obtained at 340 K. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The pressure dependence of the recombination reaction Cl + FC(O)O + M → FC(O)OCl + M has been investigated at 296 K. FC(O)O radicals and Cl atoms were generated by laser flash photodissociation of FC(O)OO(O)CF at 193 nm in mixtures with Cl2 and He or SF6 over the total pressure range 8−645 Torr. The measured FC(O)O radical and F atom yields in the photolysis are 0.33 ± 0.06 and 0.67 ± 0.06. The reaction lies in the falloff range approaching the high-pressure limit. The extrapolations toward the limiting low- and high-pressure ranges were carried out using a reduced falloff curves formalism, which includes a recent implementation for the strong-collision broadening factors. The resulting values for the low-pressure rate coefficients are (2.2 ± 0.4) × 10-28[He], (4.9 ± 0.9) × 10-28[SF6], (1.9 ± 0.3) × 10-28[Cl2] and (5.9 ± 1.1) × 10-28[FC(O)OO(O)CF] cm3 molecule-1 s-1. The derived high-pressure rate coefficient is (4.4 ± 0.8) × 10-11 cm3 molecule-1 s-1. For the reaction Cl + FC(O)OCl → Cl2 + FC(O)O a rate coefficient of (1.6 ± 0.3) × 10-11 cm3 molecule-1 s-1 was determined. The high-pressure rate coefficient was theoretically interpreted using SACM/CT calculations on an ab initio electronic potential computed at the G3S level of theory. Standard heat of formation values of −99.9 and −102.5 kcal mol-1 were computed at the G3//B3LYP/6-311++G(3df,3pd) level of theory for cis-FC(O)OCl and trans-FC(O)OCl, respectively. The computed electronic barrier for the conversion between the trans and cis conformers is 8.9 kcal mol-1. On the basis of the present results, the above reactions are expected to have a negligible impact on stratospheric ozone levels. [ABSTRACT FROM AUTHOR]