The propagation of reaction-diffusion fronts in an open liquid solution layer is critically
affected by mass transfer between the liquid solution and the adjacent gas phase.
This is the case in the iodate-arsenous acid (IAA) reaction when run under stoichiometric
excess of iodate. Here, iodine is the reaction product, which has a low solubility
in the liquid phase, hence, excess iodine rapidly evaporates. In the gas phase, it
diffuses and overtakes the reaction front propagating in the liquid medium because
its diffusion coefficient in the gas phase is considerably larger than that in aqueous
solution. Evaporated iodine is re-dissolved into the reaction medium ahead of the
reaction front. Since iodine is the autocatalytic species of the IAA reaction, this
additional gas-phase transport may lead to an acceleration of the propagating reaction
front.
