Order (chemistry) - Fractional Order

In fractional order reactions, the order is a non-integer, which often indicates a complex reaction mechanism. For example, the pyrolysis of ethanal (CH₃-CHO) into methane and carbon monoxide proceeds with an order of 1.5 with respect to ethanal: r = k3/2. The decomposition of phosgene (COCl₂) to carbon monoxide and chlorine has order 1 with respect to phosgene itself and order 0.5 with respect to chlorine: r = k 1/2.