Question

A hypothetical reaction, $A_2+B_2\to 2AB$, follows the mechanism as given below:

$A_2\rightleftharpoons A+A\left(fast\right)$
$A+B_2\to AB+B\left(slow\right)$
$A+B\to AB\left(fast\right)$

The order of the overall reaction is:

• A. 2
• B. 1
• C. 3/2
• D. 0

Answer 1

The correct option is C 3/2

Here the A is an intermediate.

$r=k\left[A\right]\left[B_2\right]$

and $K_c=\frac{\left[A\right]\left[A\right]}{\left[A_2\right]}$ or $\left[A\right]=K_c^{\frac{1}{2}}[A_2{]}^{\frac{1}{2}}$

Thus $r=k\times K_c^{\frac{1}{2}}\left[A_2{]}^{\frac{1}{2}}\right[B_2]$

$rate=k\left[A_2{]}^{\frac{1}{2}}\right[B_2]$ or over all order is 3/2.