2002 AIPMT Chemical KineticsRate of a Reaction Easy Question 1 of 2 in Rate of a Reaction

$3A \rightarrow 2B$, rate of reaction $+\dfrac{d[B]}{dt}$ is equal to : -

A $-\dfrac{3}{2}\dfrac{d[A]}{dt}$
B $-\dfrac{2}{3}\dfrac{d[A]}{dt}$
C $-\dfrac{1}{3}\dfrac{d[A]}{dt}$
D $+2\dfrac{d[A]}{dt}$

The answer is B.

Solution

For $3A \rightarrow 2B$, the rate of reaction $= -\dfrac{1}{3}\dfrac{d[A]}{dt} = +\dfrac{1}{2}\dfrac{d[B]}{dt}$
$\Rightarrow \dfrac{d[B]}{dt} = -\dfrac{2}{3}\dfrac{d[A]}{dt}$
For every 3 mol of A used, 2 mol of B are formed, so B is formed at $\dfrac{2}{3}$ the rate at which A disappears.

Concept Relating rates of disappearance and formation

Rate of a Reaction in past papers

2 questions from this chapter have appeared across 2 exam years.