Question

$100$ mL of pure phosphine is decomposed to produce vapours of phosphorus and $H_2$. The change in volume during reaction is :

• A. $75$
• B. $50$
• C. $25$
• D. $150$

Answer 1

Answer: (A)

$75$

$4P{H}_3\left(g\right)\to P_4\left(g\right)+6H_2\left(g\right)$
$V$ at $t=0$ $100$ $0$ $0$
$V$ at $t=t$ $0$ $\frac{100}{4}$ $\frac{6\times 100}{4}$
$=25;=150$

Here, volume $\left(V\right)$ is in mL.
New volume$=25+150=175$ mL

Change in volume $=175-100=75$ mL