Question

The reaction 2NO2(g)+F2(g)-->2NO2F(g) has an overall second order rate law, rate=k[NO2][F2]. Suggest a mechanism consistent with this rate law, being sure to label steps as fast and slow. (Hint: It is easiest to assume the first step is slow.)

Answer 1

The reason why it is easiest to assume the first step is slow is because that would be your rate determining step and would give you the rate law given in the problem. So you take the two compounds from the rate law given and put them as your two reactants in your first step: NO2 + F2 ---> NO2F + F (all gases) Your next step needs to make sense for your overall reaction. And you also need to have an intermediate which in this case will be F: F + NO2 ---> NO2F (again all gases) This is the fast step. Your intermediate cancels out to give you your overall equation: 2NO2 + F2 ---> 2NO2F (all gases)