One possible mechanism for the gas phase reaction of hydrogen with nitrogen monoxide is: step 1: H2(g) + 2 NO (g) → N2O (g) + H2O (g) step 2: N2O (g) + H2 (g) → N2 (g) + H2O (g) Identify the molecularity of each step in the mechanism. (1, 2, or 3) Step 1 Step 2

step 1 is trimolecular while step 2 is bimolecular.

Explanation:

Molecularity of an elementary reaction is defined the number of molecules that come together to react in a given elementary (single-step) reaction. It is equal to the sum of stoichiometric coefficients of reactants in that elementary reaction. Depending on the number of molecules that come together in an elementary step, a reaction can be designated as; unimolecular, bimolecular or trimolecular.

The kinetic order of any elementary reaction or reaction step is equal to its molecularity, and the rate equation of an elementary reaction can easily be determined by inspection, from the molecularity.

For a complex (multistep) reaction, the kinetic order of reaction is not determined from the molecularity since molecularity only describes elementary reactions or steps.

From our discussion above we can see that, step 1 is trimolecular while step 2 is bimolecular.