Mechanism of a hypothetical reaction
`X_(2) + Y_(2) rarr 2XY` is given below:
(i) `X_(2) rarr X + X` (fast)
(ii) `X+Y_(2) hArr XY+Y` (slow)
(iii) `X + Y rarr XY` (fast)
The overall order of the reaction will be :

Options

A. 2
B. 0
C. `1.5`
D. 1

Answer

C

Explanation

c) The solution to this problem is given by assuming step (i) to be of reversible nature which in not given in the data.
Oveall rate = Rate of the slowest step
`k[X][Y_(2)]`……….(i)
Equilibrium constant to the fast step (i)
`K=[X]^(2)/[X_(2)]`, or `X = sqrt(K[X_(2)])`...........(ii)
By substituting value of X in eqn. (i), we get
Overall rate (k) `=sqrt(K[X_(2)])[Y_(2)] = k^(')[X_(2)]^(1/2)[Y_(2)]`
Order of reaction `=1/2 +1=3//2` or 1.5