Question

One mole of benzene (component 1) is mixed with two moles of toluene (component 2). At 60 °C the vapor pressures of benzene and toluene are 51.3 and 18.5 kPa, respectively a) As the pressure is reduced, at what pressure will boiling begin? b) What will be the composition of the first bubble of vapor? c) If the pressure is reduced further, at what pressure does the last trace of liquid disappear? d) What is the composition of the last trace of liquid?

Answer 1

Imole of Benzene (A) Mr X Lure 2 more of Toluene (B) use Rault's low: Psoin = XAPO + Xo På = 12 x 51.3 + 2 x 18.5 = 29.43 kPa At 29.43 kPq first drop will form (a) (6) Now, PA = XAPA = 17.1 kPa PB = X8PB = 3 x 18.5 = 12.33 kPa Plotas = 29.43 kPa = 10.5 Protal 29.43 tonal - - 0.58 Total in vapour Phase. mole fraction of Benzene JB = 1- y = 0.42 0.42

(c) Now, it last trace of liquid is remaining, then, Composition of vapour phase will be same as initial Composition of liquid Phase . .. YA = } 1343 so that CP= Presure or soln. PA = Pressure of Pure Benzene, to list saisis A 2 3x 51.3 3x18.5 + 2x153.9 55.5 183.9 363.3 x 55.5 153-9x55.5 = P = 153.9x55.5 ² = 23.51 pkg. 363.3 (d) PA = YAPTotal = 4A PA Partial pressure of Benzene :-) x = 1 x 235 20.152 513 mole trachon of Benzene in last trace of land

.1-0.152 = 0.848 mole fraction of Toluene