OCR Text |
Show HS03 + M = SOe + OH -+ M The other part of the reaction mechanism consists of·-the complex chain branching mechanism by which methanol oxidizes, i.e. this part of the mechanism determines the supply of free radicals for the nonbranching reaction mechanism above. Thus the error in the temperature at which the reaction occurs ~ay reflect an omission from the model of some important initiating or chain branching processes. The experimental data in Figure 4 show that when S03 and NO are both present in a mixture, the SOa reduction is slower by a factor of 0.28 while the computer modeling results in Figure 8 show the rate of SO. reduction to be 0.761 times that of NO conversion. Within the model the ratio of these-rates 'corresponds to the ratio of the rate constants for the reactions HOe + NO = OH +NOe and HOe + S03 = HS~ + De. 5ince the rate constant for the reaction HOe + NO = OH +NOa is fairly well established, the disagreement between the modeling and experiment presumably relates to the rate constant for HO. + S~ = HS~ + 0., i.e. the experimental data indicate that it's somewhat slower than the rate assumed in the ~odel. Within the model the rate constant for HOe + 5~ = HSO. + Oe is calculated from apparently reliable measurements of the reverse rate constant (14), and the equilibrium constant for the reaction. While the thermodynamics of HOe, S03, and De are all well established, the heat of formation of HS03 is available only as an estimate by Benson (15). This estimate has been criticized (16), and if one accepts a value of the heat of formation of HS03 that makes HOe + 50. = HSo. + De a slightly endothermic reaction the conflict between the modeling and the experimental data can be resolved. Conclusions Computer modeling predicts the existence of a previously unknown rapid homogeneous gas phase reaction in which 503 is selectively reduced to 50e and NO is oxidized to NOe • These predictions have been qualitatively confirmed by experiment. Part of the quantitative disagreement between the model predictions and experiment may be due to uncertainties in the heat of formation of HSOa • Acknowledge This work was supported by the National Science Foundation under a Phase 1 Small Business Inovation Research grant, award number 151-8760344. |