Question

A closed vessel contains equal number of molecules of $N_2$ and $O_2$ at a total pressure of 650 mm of Hg. If $N_2$ is completely removed, the pressure in mm of Hg will:

• A. drop to 650/3
• B. drop to 650/2
• C. remain unchanged
• D. become $650\times 2$

Answer 1

The correct option is B drop to 650/2

Equal number of molecules means equal number of moles i.e, they both have a mole fraction of $\frac{1}{2}$.
Since, partial pressure $\propto$ mole fraction
$\therefore P_{N_2}=P_{O_2}$
$P_{O_2}=\frac{650}{2}$ mm of Hg