CGPET 2013 Solved Paper

For the reaction,
2‌NO+Br2⟶2‌NOBr
the following mechanism has been given
NO+Br2‌

‌ Fast ‌

⟶

NOBr2 . . . (i)
NOBr2+NO‌

‌ Slow ‌

⟶

2‌NOBr . . . (ii)
As the second step is the rate determining step,
‌ Rate ‌=k′[NOBr2][NO] . . . (iii)
From (i) step
k′′=‌

[NOBr2]

[NO][Br2]

or [NOBr2]=k′′[NO][Br2] . . . (iv)
By substituting this value in rate law step (iii), we get
‌ Rate ‌=k′k′′[NO]2[Br2]
or Rate =k′′[NO]2[Br2]