Question

The rate law of a reaction is $\text{Rate}=k[A][B]^2$. If the concentration of $B$ is trebled keeping $[A]$ constant, the rate becomes

• A. double
• B. trebled
• C. quadrupled
• D. nine times

Hint:

If $\text{Rate}\propto [X]^n$, multiplying $[X]$ by $m$ multiplies the rate by $m^n$.

Answer 1

The Correct Option is D

Step 1: Apply the rate law.
Initial rate $r_1 = k[A][B]^2$. If $[B]\to 3[B]$ and $[A]$ constant, new rate
$r_2 = k[A](3[B])^2 = 9\,k[A][B]^2 = 9r_1$.
Step 2: Conclusion.
Rate increases by a factor of 9 $\Rightarrow$ nine times.