To an evacuated vessel with movable piston under external pressure of 1 atm., 0.1 mol of He and 1.0 mol of an unknown compound (vapour pressure 0.68 atm . at $0^{\circ} \mathrm{C}$ ) are introduced. Considering the ideal gas behaviour, the total volume (in litre) of the gases at $0^{\circ} \mathrm{C}$ is close to

JEE Advanced · 2011 · 10 Apr 2011 · Paper 1 · States of Matter

To an evacuated vessel with movable piston under external pressure of 1 atm., 0.1 mol of He and 1.0 mol of an unknown compound (vapour pressure 0.68 atm . at

0^{\circ} C

) are introduced. Considering the ideal gas behaviour, the total volume (in litre) of the gases at

0^{\circ} C

is close to

Answer: 7

Solution

The unknown compound has vapor pressure 0.68 atm, so it will not completely vaporize at 1 atm external pressure. Only He behaves as an ideal gas.

For He, the pressure inside = 1 - 0.68 = 0.32 atm (equilibrium with vapor pressure of unknown compound)

Using ideal gas equation for He:

P V = n R T

0.32 \times V = 0.1 \times 0.0821 \times 273

V = \frac{0.1 \times 0.0821 \times 273}{0.32} \approx 7 L

JEE Advanced · 2011 · 10 Apr 2011 · Paper 1 · Integer answer

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