Thereaction 2 NO + O 2 2 NO 2 obeys the rate law -?[O 2 ] / ?t = k obsd [NO] 2 [
ID: 683367 • Letter: T
Question
Thereaction 2 NO + O2 2 NO2 obeys the rate law
-?[O2] / ?t = kobsd[NO]2[O2]
Which ofthe following mechanisms is consistent with the experimental ratelaw?
A) NO + NO N2O2 (slow)
N2O2 + O2 2NO2 (fast)
B) NO + O2 NO3 (fast equilibrium)
NO3 + NO 2NO2 (slow)
C) 2NO N2O2 (fast equilibrium)
N2O2 NO2 + O (slow)
NO + O NO2 (fast)
D) O2 + O2 O2 + O2 (slow)
O2 + NO NO2 + O (fast)
NO + O NO2 (fast)
Please explain why B would be the best answer.
Explanation / Answer
We Know that : The given Reaction is : 2NO + O2 2NO2 - [ O2] / t = K [ NO ]2[ O2 ] The above Rate law is bestdescribed as : NO + O2 NO3 (fast equilibrium) NO3 + NO 2NO2 (slow)Considerthe First Reaction Proceeds with Rate constant asK1 and the Second Reaction Proceeds with Rateconstant K2. From the above Reaction it is clear that : [ NO3] acts as intermediate so we can apply the steady-stateapproximation to NO3 Rate = K [ NO ] [ NO3 ] = K [ NO ] x K1 [ NO ] [ O2] = K' [ NO ]2 [ O2]
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