The breakdown of benzene, ethylbenzene, styrene, and o-chlorotoluene in aqueous solution by 520 Mit ultrasonic waves was studied at various initial concentrations in the millimolar range. First-order reaction rates depend upon both initial concentration and sonication time. These variations can be explained by a model that combines some physical and chemical aspects of sonochemistry. The basic assumptions of the model are first-order pyrolysis in the cavitations yielding both reactive/volatile and inert/nonvolatile products, and lowering of the maximum cavitation temperature due to the presence of the organic compounds in the bubble phase, Despite the necessary assumptions and approximations in order to limit the number of adjustable parameters, the lack of fit standard deviation after regression-was as low as 4-9.2%.