Question

2gm of $O_2$ at ${27}^{\circ }$C and 760mm of Hg pressure has volume

• A. 1.5 lit.
• B. 2.8 lit.
• C. 11.2 lit.
• D. 22.4 lit.

Answer 1

The correct option is A 1.5 lit.

PV = nRT
$\Rightarrow$ V = $\frac{nRT}{P}=\frac{\frac{2}{32}\times 0.0821\times (27+273)}{\frac{760}{760}}L$ = 1.53 L

Note:Unit of parameters must be chosen judiciously.
Taking R = 0.0821 atm L $mol{e}^{-1}{K}^{-1}$ and Pressure in atm will give volume in litres
While taking all values in SI unit i.e. R = 8.314 J $mol{e}^{-1}{K}^{-1}$ and Pressure in pascal will give volume in $m^3$

Points to remember:
R = 0.821 atm L $mol{e}^{-1}{K}^{-1}$ = 8.314 J $mol{e}^{-1}{K}^{-1}$ = 2 cal $mol{e}^{-1}{K}^{-1}$
Unit of pressure: 1 atm $\approx$ 1 bar = 760 mm of Hg = 760 torr
= ${10}^5$ pascal $\left(\frac{N}{m^2}\right)$