Question

A gaseous reaction $A_2\left(g\right)\rightleftharpoons B\left(g\right)+1/2C\left(g\right)$ shows increase in the pressure from 100 mm to 120 mm in 5 min. The rate of disappearance of $A_2$ is:

• A. 4 mm $mi{n}^{-1}$
• B. 8 mm $mi{n}^{-1}$
• C. 16 mm $mi{n}^{-1}$
• D. 2 mm $mi{n}^{-1}$

Answer 1

The correct option is B 8 mm $mi{n}^{-1}$

$A_2\to B\left(g\right)+1/2C\left(g\right)$
Here, the pressure is, initially 100 0 0
At reaction time, pressure 100-x x 1/2x

So, we know that,
Change in pressure, $100+1/2x=120$

So, $x=40mm$

Hence, the rate of disappearance of $A_2$ is, $\frac{-d\left[A_2\right]}{dt}$.
Here, change in time $dt=5min$So, $\frac{-d\left[A_2\right]}{dt}=\frac{40}{5}=8mm/min$.