Kinetics of oxidation of aqueous sulfur(IV) by nitrogen dioxide-猫眼课题宝

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1982

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Y. N. Lee;S. Schwartz

研究了在中性pH条件下，硫（IV）被NO/sub 2/氧化的气液反应，6.40和5.80，以及低试剂浓度，即，（S（IV））= 1 x 10/sup -6/ M和p/sub NO/sub 2//大约= 1 x 10/sup-7/ atm。在这些反应条件下发现的主要产物是H/sup +/、NO/sub 2//sup -/和SO/sub 4//sup =/，并且化学计量与2NO/sub 2/ + HSO/sub 3//sup -/ + H/sub 2/O - > 3 H/sup +/ + 2NO/sub 2//sup -/ + SO/sub 4//sup =/一致。反应速率通过使用pH统计装置跟踪酸产生来确定，作为气相和液相混合时间常数（tau/sub m/ = 1.6 - 5.3 s）的函数。反应速率被发现是显着控制的传质，即使在低试剂浓度使用，和外推到相混合条件（τ/子m/ = O）是能够只产生一个下限反应速率常数。对于根据总体二级速率表达式（R = k/sup（2）/（S（IV））（NO/sub 2/））解释的反应速率，该速率常数在pH 6.40和5.80下均为2 x 10/sup 6/ M/sup-1/ s/sup-1/。然而，有证据表明，更复杂的反应机制显然涉及中间体。在pH 6和p/sub SO/sub 2/// = p/sub NO/sub 2/// = 3 × 10/sup-9/ atm下，用二级反应速率常数下限估算了NO/sub 2/-S（IV）反应对云水产酸的贡献。虽然由于使用了k/sup（2）/的下限值和反应机制的不确定性，分析是初步的，但这样的速率将对云酸化产生重大影响。«少

The gas-liquid oxidation reaction of sulfur(IV) by NO/sub 2/ has been studied at neutral pH's, i.e., 6.40 and 5.80, and low reagent concentrations, i.e., (S(IV)) approx. = 1 x 10/sup -6/ M and p/sub NO/sub 2// approx. = 1 x 10/sup -7/ atm. Major products found under these reaction conditions are H/sup +/, NO/sub 2//sup -/, and SO/sub 4//sup =/, and the stoichiometry is consistent with 2NO/sub 2/ + HSO/sub 3//sup -/ + H/sub 2/O - > 3H/sup +/ + 2NO/sub 2//sup -/ + SO/sub 4//sup =/. The reaction rate was determined by following acid production via a pH-stat apparatus as a function of mixing time constant of the gas and liquid phases (tau/sub m/ = 1.6 - 5.3 s). The reaction rate was found to be significantly controlled by mass-transfer, even at the low reagent concentrations employed, and the extrapolation to the phase-mixed condition (tau/sub m/ = O) was able to yield only a lower-limit reaction rate constant. This rate constant, for reaction rate interpreted according to an overall second-order rate expression (R = k/sup (2)/ (S(IV))(NO/sub 2/)), was 2 x 10/sup 6/ M/sup -1/ s/sup -1/ at both pH 6.40 and 5.80. However, evidence is represented of amore » complex reaction mechanism apparently involving intermediates. As estimate of the contribution of NO/sub 2/-S(IV) reaction to acid production in cloud water made using the lower-limit second-order rate constant is 3 x 10/sup -5/ M hr/sup -1/ at pH 6 and p/sub SO/sub 2// = p/sub NO/sub 2// = 3 x 10/sup -9/ atm. Although the analysis is preliminary because of the use of a lower-limit value for k/sup (2)/ and the uncertainties in reaction mechanism, such a rate would constitute a significant contribution to cloud acidification.« less

Kinetics of oxidation of aqueous sulfur(IV) by nitrogen dioxide

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