categorize each mechanism given below as either plausible or Categorize each mec
ID: 636052 • Letter: C
Question
categorize each mechanism given below as either plausible or Categorize each mechanism given below as either plausible or implausible Overall Reaction: 2NO + Cb- 2NOCI Experimentally Determined Rate Law: rate = k[NO][G ]. Plausible Mechanisms: Step 1: NO+ CI2 NOCI + CI (slow) Step 2: NOCI+ NO NOCIz (fast) Step 1: NO +Cl2 NOCI2(slow) Step 2: NOCI2NOCI+CI (fast) Step 3: NO +CINOCI (fast Step 1: CI2 2CI Step 2: 2NO+ 2CI 2NOCI (fast) (slow) Step 1: NO + NO-N202(slow) Step 2: N202 + Ck 2NOCI (fast) Implausible Mechanisms: Step 1: NO+CI2-NOCI2 (slow) Step 2: NOCI2NO- 2NOCI (fast) Step 1: NO + CNOCI+Ci (slow) Step 2: CI+NO- -NOCI (fast)Explanation / Answer
Ans ) Final equation in all cases should be 2NO (g) + Cl2 (g) ------ 2NOCl (g).
By elimination in all the mechanisms we get the final equation the same.
But there are some discrepancies ----
In 1st case:
NO(g) + Cl2 (g) --- NOCl + Cl ; Reaction is given as slow, however it is fast reaction.
NOCl2 + NO ---- 2NOCl ; Reaction is given as fast, however it is a slow reaction.
Thus, the rate determining step is NOCl + NO ---- 2NOCl.
Therefore, the first case is an implausible mechanism.
In 2 nd case : NO + Cl2 is given as slow, however it is a fast reaction.
The rate determining equation should have been NOCl2 --- NOCl + Cl as it is slow. But the reaction is given as fast. Hence the 2 ND case too is also an implausible mechanism.
In 3rd case: It is implausible mechanism.
In 4th case: It is also implausible mechanism.
In 5TH case : THIS IS A PLAUSIBLE MECHANISM .
NO + Cl2 ---- NOCl2
NOCl2 + NO ---- 2NOCl.
However, NOCl2 + NO is the slow reaction and rate determining step.
rate of reaction r = k[NOCl2][NO]
NOCl2 is a reaction intermediate and so we should use the equillibrium constant to eliminate the intermediate.
Kc = [NOCl2]/[NO][Cl2]
so, [NOCl2] = Kc [NO][Cl2]
or, r = kKc[NO][Cl2][NO]
or, r = k' [NO]^2 [Cl2] ; this is the final rate law.
In 6th case,
It is an implausible mechanism.
So, we can observe that the reaction mechanism in the 5th case is a feasible one and should be considered as Plausible mechanism.
In 3rd case :
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