Question

The vapour pressure of two liquids $P$ and $Q$ are $80$ torr and $60$ torr respectively. The total vapour pressure obtained by mixing $3$ mole of P and $2$ mole of $Q$ would be:

• A. $68$ torr
• B. $20$ torr
• C. $140$ torr
• D. $72$ torr

Answer 1

Answer: (D)

$72$ torr

Mole fraction of $P\left(X_P\right)=\frac{3}{3+2}=35$

Mole fraction of $Q\left(X_Q\right)=\frac{2}{3+2}=\frac{2}{5}$

Now, Total vapour pressure $\left(P_T\right)=X_P{P}_P+X_Q{P}_Q$

$=\frac{3}{5}\times 80+\frac{2}{5}\times 60$

$\therefore$ Total vapour pressure $\left(P_T\right)=72torr$