As described in Non-integer Stoichiometric Coefficients and Reactions with Arbitrary Reaction Order , respectively, Surface Kinetics reaction expressions can included non-integer stoichiometric coefficients for participating species and arbitrary, user-specified reaction orders for any species in the system.

The user is advised to exercise caution when specifying a change of reaction order. Such a change may produce unexpected and unphysical results in a kinetic simulation. The user should also consider the kinetics of the reverse reaction when changing reaction orders for the forward reaction.