Question
Nitric oxide, NO, reacts with oxygen to produce nitrogen dioxide,
2NO(g) + O2(g) → 2NO2(g)
What is the predicted rate law, if the mechanism is
Solution
The slow step is the rate determining step. In the slow step in this reaction, 1 molecule of NO3 (intermediate) and 1 molecule of NO combine to form the products. Therefore, rate of this reaction depends upon 1 concentration term of NO3 and 1 concentration term of NO.
∴ Molecularity of the reaction = 1 + 1 = 2.
Rate = K [NO3] [NO]
NO3 is an intermediate which is formed rapidly by the collision of 1 molecule of NO and 1 molecule of O2.
[NO3] ∝ [NO][O2]
Rate = K1 [NO3] [NO]
= K [NO] [O2] [NO]
= K [NO]2[O2]
Order of reaction is 2 + 1 = 3.
