Question

$4\text{g}$ of an ideal gas was introduced into a bulb of volume of $0.821{\text{dm}}^3$ at certain pressure, $P$ and temperature $T$. The above bulb was placed in a thermostat mentioned at temperature $(T+125)K$ of $0.8\text{gm}$ of the gas was left off to keep the original pressure. Calculate the pressure in atmosphere. [Molecular weight of the gas is $40{\text{g mole}}^{-1}$ and $R$ value is $0.0821{\text{lit-atm-k}}^{-1}\text{mol}$]

Answer 1

Initial no.of moles $\left(n\right)=\frac{4}{40}=0.1$
Final no.of moles $\left(n\right)=\frac{3.2}{40}=0.08$
Since $P$ and $V$ are constant
$n_1{T}_1=n_2{T}_2$
$0.1T_1=0.08(T_1+125)$
$T_1=500K$
From ,
$PV=nRT$
$P=\frac{0.1\times 0.0821\times 500}{0.821}=5\text{atm}$