Question

8.3 A solution of 35 mole % aniline and 65 mole % hexane is cooled from a high temperature. Phase separation occurs at 56.5°C. Aniline and hexane obey regular solution theory. (a) What is the interaction energy S2? (b) What is the critical solution temperature? (c) The vapor pressure of pure aniline and pure hexane at 70°C are 0.011 atm and 1.11 atm, respectively. What is the total pressure of a 50 mole % mixture at this temperature?

Answer 1

(a) Interaction energy is defined as the contribution to the total energy that is caused by an interaction between the considered molecules .It depends on the relative position and charge.

(b) Critical solution temperature is defined as the temperature at which complete miscibility is reached as the temperature is raised or in some cases lowered —used of two liquids that are partially miscible under ordinary conditions.

(c) Given,

Mole % of aniline = 35

Mole % of hexane = 65

Vapor pressure of pure aniline, P_A⁰ = 0.011 atm

Vapor pressure of pure hexane, P_B⁰ = 1.11 atm

Total pressure of a 50 mole % mixture = ?

We have the equation,

P_A = P_A⁰X_A

= 0.011 x ( 35/50)

= 0.011 x 0.7

= 7.7 x 10^-3

P_B = P_B⁰X_B

= 1.11 x ( 65/50)

= 1.11 x 1.3

= 1.443

Daltons law, Total Pressure = sum of individual vapour pressure

P_Total = P_A + P_B

= 7.7 x 10^-3 + 1.443

= 1.4507 atm