Chemistry - Chemical Kinetics Question with Solution | TestHub

Given the rate law $r=k[A][B]$.

Let the initial rate be $r_1=k[A][B]$.

Checking the given options:

If the concentration of both A and B are doubled, $r_2=k(2[A])(2[B])=4k[A][B]=4r_1$.

If the concentration of A is doubled and the concentration of B is kept constant, $r_2=k(2[A])[B]=2k[A][B]=2r_1$.

If the concentration of B is doubled and the concentration of A is halved, $r_2=k\left(\frac{[A]}{2}\right)(2[B])=k[A][B]=r_1$.

If the concentration of A is kept constant and the concentration of B is halved, $r_2=k[A]\left(\frac{[B]}{2}\right)=\frac{1}{2}k[A][B]=\frac{r_1}{2}$.

Thus, the rate of reaction doubles when the concentration of A is doubled and the concentration of B is kept constant.

Answer: Concentration of $A$ is doubled and concentration of $B$ is kept constant.