where A (m2 ) is the interfacial area, V (m3 ) is the solution volume, k0 (m s1 ) is the pseudo-first-order reaction rate constant (k 0 ¼ k COH), and km (m s1 ) is the mass transfer coefficient of the solute (km = D/L, where D (m2 s1 ) is the solute diffusivity and L (m) is the thickness of the interfacial zone). Note that the fractional term in Eq. (4) is equal to the measured kobs.
One way to support the validity of the proposed rate equation is to show that kobs is proportional to A, which requires that the interfacial area be varied while keeping km and k0 constant. Recalling that km = D/L, it is reasonable to assume that D is independent of A, as it is primarily determined by the characteristics of the particular solute. L has been defined as the thickness of the interfacial zone, which is effectively determined by the diffusion distance of the active species (i.e., OH radicals). The diffusion distance (estimated to be 6–20 nm) is primarily influenced by the concentration of OH radicals (see discussion in Section 3.4) and the density of the liquid, which is not likely to change dramatically with variations in A [6,17]. k0 varies with the OH radical concentration, which could also depend on A (see Section 3.4).
reaction [16]: