Question

A sample of air is saturated with benzene (vapour pressure =100 mm Hg at 298 K) at 298K, 750mm Hg pressure. If it is isothermally compressed to one third of its initial volume, the final pressure of the system is:

• A. $2250$ torr
• B. $2150$ torr
• C. $2050$ torr
• D. $1950$ torr

Answer 1

The correct option is C $2050$ torr

The total pressure is equal to the vapour pressure of benzene and the pressure of air.

The pressure of air $=750-100=650mm$ of Hg.

The mixture is compressed to one-third of its volume.

Now,

Since, $P\propto \frac{1}{V}$

So, pressure of the air after compression, $P_f=650\times \text{3 mm of Hg}=\text{1950 mm of Hg}$

The final total pressure $P_T=(1950+100)=2050mm$ of Hg. $=2050torr$

$\because$ 1 mm of Hg $\approx$ 1 torr

Hence, the correct option is $C$