A detailed radical reaction model, both homogeneous and heterogeneous, is shown to describe quantitatively published initial rates of the pyrolysis of 1,2-dichloroethane in the gas phase. These data were obtained in conditioned static reactors with different surfaceto-volume ratios, in the absence (at 703 K) and presence (at 572 K) of chlorine. The pressures of 1,2-dichloroethane and chlorine vary from 20 to 500 torr and from 0 to 16 torr, respectively.