Interaction of Sound with Gas Phase Reactions

Abstract

Reaction and sound propagation are coupled in ideal gas phase reactions which have a difference in the sums of stoichiometric coefficients of reactants and products, or which have a pressure-dependent rate coefficient. Numerical and approximate analytical (WKB-type) solutions are obtained for the hydro-dynamic equations which take into account this coupling and which describe the spatial and temporal variations in density, velocity and concentration for an isothermal system far from equilibrium. Specific results are given for a unimolecular reaction of the type A → B+C, where sound is shown to be amplified in both high and low pressure regions, with an accompanying change in frequency; the system is unstable to small perturbations. Possible applications include a new method for the determination of rate coefficients by acoustic means.