PYQ NEET- Chemical Thermodynamics L-3

Question: A vessel contains $3.2 \mathrm{~g}$ of dioxygen gas at STP $(273.15 \mathrm{~K}$ and $1 \mathrm{~atm}$ pressure). The gas is now transferred to another vessel at constant temperature, where pressure becomes one third of the original pressure. The volume of new vessel in L is : (Given : molar volume at STP is $22.4 \mathrm{~L}$ )#

A) 67.2

B) 6.72

C) 2.24

D) 22.4

Answer: 6.72#

Solution:#

At constant temperature and amount $$ \begin{aligned} & P_1 V_1=P_2 V_2 \ & P_1 V_1=\frac{P_1}{3} V_2\left[\therefore P_2=\frac{P_1}{3}\right] \ & V_2=3 V_1 \end{aligned} $$ mole of $O_2(g)=\frac{3.2}{32}=0.1$ mole Volume of $O_2(g)=(0.1 \times 22.4) \mathrm{L}=2.24 \mathrm{~L}$

At STP $\left(\mathrm{V}_1\right)$ $$ \begin{aligned} & V_2=3 V_1=3 \times 2.24 \ & =6.72 \mathrm{~L} \end{aligned} $$