Question

The reading of pressure gauge at which only liquid phase exists is:

• A. $499$ mm of Hg
• B. $399$ mm of Hg
• C. $299$ mm of Hg
• D. none of the above

Answer 1

The correct option is D none of the above

$X_A=0.75,X_B=0.25$
Above 500 mm Hg, only liquid phase exists.

$P_{bubblepoint}=X_A{P}_A^o+X_B{P}_B^o$

$=0.75\times 400+0.25\times 800=500mm$.

$y_A=0.75,y_B=0.25$

At dew point,

$\frac{1}{P_T}=\frac{y_A}{P_A^o}+\frac{y_B}{P_B^o}\Rightarrow \frac{1}{P_T}=\frac{0.75}{400}+\frac{0.25}{800}=\frac{1.5+0.25}{800}$

$\Rightarrow P_T=\frac{800}{1.75}=457.14mmofHg$
Below dew point point only vapour phase exists.