Question

An equimolar mixture of benzene and toluene is contained in a piston/cylinder arrangement at a temperature T. What is the maximum pressure below which the mixture exists as a vapour phase alone? At the given T, the vapour pressures of benzene and toluene are 203.9 kPa and 85.3 kPa, respectively. Assume that Raoult’s law is valid.

Answer 1

Given, 

Vapour Pressure of benzen and to toluene are 203.9 kpa and 85.3 kpa respectively.

∵ mixture exists as a vapour phase alone in cylinder it means equimoles of benzen and to we exit in vapour phase.

therefore using Raoults's law-

P_total = x_ben . p_ben + x_tol p_tol

P_total = \((\frac{1}{2}\times203.9\times10^3+\frac{1}{2}\times85.3\times10^3)pa\)

= (101.95 x 10³ + 42.65 x 10³)

= 144.6x10³ pa

P_total = 144.6 kPa

Hence maximum Pressure in cyclinder at temperature

T = 144.6 KPa.