Question

How much will the rate of the reaction $2A+B\to A_{2}B$ change, if the concentration of substance $A$ is doubled and that of substance $B$ is halved?

• A. Halved
• B. Doubled
• C. Tripled
• D. Remains same

Answer 1

The correct option is B Doubled

If the concentration of B is halved then

$\left[B\right]=\frac{1}{2}[B{]}_0$

where $[B{]}_0$ is the initial concentration of B.

Similarly, $\left[A\right]=2[A{]}_0$

For the given reaction

Rate, $r=k\left[A{]}^2\right[B]$

$r_0=k\left[A{]}_0^2\right[B{]}_0$

$r_f=\frac{4}{2}k\times \left[A{]}_0^2\right[B{]}_0=2r_0\Rightarrow$ Rate doubled.