1.

A reaction proceeds by a two step mechanism A_2underset(k_2)overset(k_1)hArr2A (fast reaction) A+B to Products (slow reaction) What is the rate law for the overallreaction ?

Answer»

rate `=k[A_2][B]`
rate `=k[A_2]^2[B]`
rate `=k[A_2]^(1/2)`
rate `=k[A_2]^(1/2)[B]`

Solution :From `A_(2) to 2 A` (FAST reaction )
`k = ([A]^(2))/([A_(2)]) or [A]^(2) = k XX [A_(2)]`
or `A = sqrt(k xx [A_(2)]) "" … (i)`
Form ` A + B to` Products (slow reaction ) , the rate LAW is :` (dx)/(dt) = k [A] [ B]`
Substituting the value of [A] from (i) in (II) ,
`(dx)/(dt) = "rate" = k sqrt(k xx [ A_(2)]) xx [B]`
`= k xx sqrtk xx [A_(2)]^(1//2) xx [ B]= k [A_(2)]^(1//2) xx [B]`


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