Question

Observe the following reaction ;
$\, \, \, \, \, \, \, \, \, \, \, A(g) + 3B(g) \longrightarrow \, \, 2C(g)$
The rate of this reaction $\big(-\frac{d [A]}{dt}\big)$ is
$3 \times 10^{-3} \, mol \, L^{-1} \, min^{-1}.$ What is thd value of $-\frac{d [B]}{dt}$ in
$mol \, L^{-1} \, min^{-1}$?

• A. $3 \times 10^{-3}$
• B. $9 \times 10^{-3}$
• C. $10^{-3}$
• D. $1.5 \times 10^{-3}$

Answer 1

Answer: (B)

The rationalised rate =
$ -\frac{d [A]}{dt} = -\frac{1}{3} \frac{d [B]}{dt} = \frac{1}{2} \frac{d [C]}{dt}$
From this relation we have
$ -\frac{d [B]}{dt} = -3 \times \frac{d [A]}{dt}$
$ = -3 \times 3 \times 10^{-3}$
$ = 9 \times 10^{-3}$