Reaction Kinetics of Nitrogen Dioxide with Liquid Water at Low Partial Pressure

Article abstract of DOI:10.1021/j150607a022

The reaction 2NO2(g) + H2O(l) ---> 2H⁺ + NO3^- + NO2^- (1) has been studied for 1E-7 < p_NO2 <8E-4 atm.Since this reaction involves the transfer of a reactant from the gas into the aqueous phase, the rate depends upon the following: (a) physical mass transfer of the reactant, (b) the equilibrium solubility of NO2, and (c) homogeneous aqueous-phase kinetics.In order for the observed rate to yield information most sensitive to (c), the rate of (a) must be comparable to that of (c).In the case of a second-order reaction, this can be achieved by working at low partial pressure of NO2 as well as a high rate of physical mixing of the two phases.To facilitate the latter, the gas was brought into contact with the liquid as finely dispersed bubbles produced by flowing through a disc-frit; the mass transfer time constant, determined by uptake of CO2, was τ_m = 1.7 - 5.3 s.The rate of reaction 1, monitored by observing the electrical conductivity of the aqueous solution, exhibited dependence on p_NO2 and τ_m consistent with second-order kinetics and a steady-state aqueous-phase NO2 concentration.Values of H_NO2, the Henry's law coefficient, and k₁, the second-order aqueous-phase rate constant, were determined to be (7.0+/-0.5)E-3 M atm^-1 and (1.0+/-0.1)E8 M^-1 s^-1, respectively, at 22 deg C.Self-consistency of the gas-liquid reaction model has been demonstrated in terms of the identity of the diffusing species and the extent of mass-transport limitation.