Question

If the above process is repeated for all other compositions of mixture of C and B. If all the points where vapours start converting into liquid are connected and all the points where vapours get completely converted into liquid are connected then obtained graph will look like.

• A. a
• B. b-
• C. c-
• D. d-

Answer 1

Answer: (B)

b-

When liquid just starts forming vapors, Raoult's law is applicable.The mole fractions in liquid state will be $X_b$ and $X_c$.
When such points are collected, the curve obtained will have equation
$P=X_B^l{P}_B^o+X_C^l{P}_C^o=X_B^l{P}_B^o+(1-X_B^l)P_C^o=P_C^o+(P_B^o-P_C^o)X_B^l=P_C^o+(P_B^o-P_C^o)X_B$
The second curve is not a straight line.
It has equation $P=\frac{P_B^o-P_C^o}{X_B^l(P_C^o-P_B^o)+P_B^o}$