A mathematical model of an electrochemical reactor is developed in which the reaction is initially between a gaseous, organic species and an inorganic oxidant which is generated electrochemically, In the electrolyte solution several chemical reactions occur, leading to several organic and inorganic compounds. The model accounts for the mass transfer processes occurring at the electrode/electrolyte interface, where chemical reactions also occur, and at the gas/liquid interface, ie the absorption and desorption processes. The model is used to simulate the behaviour of a single stage cell and a multi-stage cell. The reaction between anodically generated chlorine and ethylene gas is used to illustrate the system behaviour.