Question

A reaction : $2A\left(g\right)+3B\left(g\right)\to C\left(g\right)$ obeys the following rate law. Rate of reaction $=\left[A{]}^3\right[B{]}^{-2}$
Select the incorrect options.

• A. The reaction will occur in a single step.
• B. If concentration of 'A' and 'B' both doubled, then rate will increase to double the original value.
• C. If 'B' is taken in very large amount as compared to 'A' then half-life of the reaction will be inversely dependent on cube of its intial concentration.
• D. If both 'A' and 'B' are taken in equal concentration then half-life will be dependent on their concentration.

Answer 1

Answer: (A), (C)

If 'B' is taken in very large amount as compared to 'A' then half-life of the reaction will be inversely dependent on cube of its intial concentration.

It is complicated reaction so, will take place in more than one step.
Rate of reaction $r=k\left[A{]}^3\right[B{]}^{-2}$
When conc. of A and B doubled then
$\text{rate}{r}_1=k\left[2A{]}^3\right[2B{]}^{-2}$
$r_1=2k\left[A{]}^3\right[B{]}^{-2}$
$\therefore r_1=2r$
If B taken in very large amount, then
$\text{rate}=k[A{]}^3$
order of the reaction $=3$
So, half - life $t_{{}_{1/2}}=\frac{1}{[A_0{]}^2}$
If both A and B are taken in equal conc. then $t_{1/2}\left[A\right]=t_{1/2}\left[B\right].$ So, it will depend on their concentration.