Question

The reaction of hydrogen an iodine monochloride is given as
$H_{2(g)}+2IC{l}_{(g)}\to 2HC{l}_{(g)}+I_{2(g)}$
This reaction is of first order with respect to $H_{2(g)}$ and $IC{l}_{(g)}$, following mechanisms were proposed
Mechanism $A$:
$H_{2(g)}+2IC{l}_{(g)}\to 2HC{l}_{(g)}+I_{2(g)}$
Mechanism $B$ :
$H_{2(g)}+IC{l}_{(g)}\to HC{l}_{(g)}+H{I}_{(g)};$ Slow
$H{I}_{(g)}+IC{l}_{(g)}\to HC{l}_{(g)}+I_{2(g)};$ Fast
Which of the above mechanism $(s)$ can be consistent with the given information about the reaction:

• A. Only B
• B. Both A and B
• C. Neither A nor B
• D. Only A

Answer 1

Answer: (A)

In the reactions which take place in a number of steps, the slowest step is known as the rate determining step. Hence, rate of reaction always depends on slow step .$H_2(g)+ICI(g)⟶HCI(g)+HI(g)$ is first order reaction with respect to $H_2$ and ICI. Thus, the mechanism B will be more consistent with the given information.