Bimolecular Elementary Reactions

A bimolecular reaction involves two reactant species, for example:




For the first type, in which the two reactant molecules are different, the rate law is first-order in A and first order in B (second-order overall):


For the second type, in which two identical molecules collide and react, the rate law is second order in A:


Some chemical reactions occur by mechanisms that consist of a single bimolecular elementary reaction. One example is the reaction of nitrogen dioxide with carbon monoxide:


(see [link])

The probable mechanism for the reaction between NO2 and CO to yield NO and CO2.

Bimolecular elementary reactions may also be involved as steps in a multistep reaction mechanism. The reaction of atomic oxygen with ozone is the second step of the two-step ozone decomposition mechanism discussed earlier in this section: