Question

In a reaction A+B $\to$ products, the rate of reaction is doubled when the concentration of A is doubled and B is kept constant and the rate of the reaction is increased by 8 times when the concentrations of both A and B are doubled, thus overall order of the reaction is:

• A. 1
• B. 2
• C. 3
• D. 0

Answer 1

Answer: (C)

3

The expression for the rate of the reaction is $r=k\left[A{]}^n\right[B{]}^m-\left(1\right)$

When the concentration of A is doubled and the concentration of B remains same, the rate expression becomes $2r=k\left[2A{]}^n\right[B{]}^m-\left(2\right)$

When the concentration of both A and B is doubled, the rate expression becomes $8r=k\left[2A{]}^n\right[2B{]}^m-\left(3\right)$

Divide equation (2) with equation (1) to obtain $n=1$

Divide equation (3) with equation (1) to obtain $n+m=3$

Hence, $m=2$

The overall order of the reaction is $=1+2=3$.

Option C is correct.