The law of mass action has been extended to include imperfect mixing and dead-zone effects in nonlinear chemical systems. It is concluded that if there is more concentration difference between two homogeneous layers in an incompletely mixed inhomogeneous solution obeying nonlinear kinetic laws, the reaction rate also is increased compared to that calculated on the basis of average reactant concentrations for homogeneous mixing. The presence of an unmixed dead-zone enhances this effect further.