AbstractThe rate law −d[O3]/dt=k1[A][O3] +k3[A][O3]2/ (k4+k5[O2]) has been found to obtain for the reaction of ozone with allene and with 1,2‐butadiene. We now find that this rate law also applies to the reaction of ozone with ethylene and presumably with all lower alkenes. This generalizes the inhibiting effect of oxygen and accounts for the simplifed rate law found in the presence of excess oxygen. Oxygen itself is a product of the ozone–ethylene reaction, and we find that as [O3]0increases, the (O2formed)/(O3used) ratio approaches 1.5. Values ofk1,k3/k5for ethylene are compared with those for allene, 1,3‐butadiene, and propene. A generalized mechanism is postulated for the reaction of ozone with alkenes involving a chain sequence that produces oxygen and which accounts for the observed rate law. A specific mechanism is postulated for the reaction of O3with ethylene, and the thermochemistry of the chain sequence is examined in