Question

For the elementary reaction, $M\to N$, the rate of disappearance of M increases by a factor of 8 upon doubling the concentration of M. The order of the reaction with respect to M is

• A. 4
• B. 3
• C. 2
• D. 1

Answer 1

The correct option is B

3

For the elementary reaction, $M\to N$

Rate law can be written as

Rate $\propto [M{]}^n$
Rate $=K[M{]}^n$

When we double the concentration of [M], rate becomes 8 times, hence new rate law can be written as

$8\times Rate=K[2M{]}^n$

$\Rightarrow \frac{Rate}{8\times Rate}=\frac{k[M{]}^n}{K[2M{]}^n}$

$\Rightarrow \frac{1}{8}=\frac{1}{[2{]}^n}$

$\Rightarrow [2{]}^n=8=[2{]}^3\Rightarrow n=3$