Question

1. 1 kg of benzene and 1 kg of toluene are mixed and maintained at 60°C. The vapor pressures of the pure components at 60°C of benzene and toluene are 53 and 18.5 kPa, respectively.
   1. If the pressure is to be reduced, predict the pressure at which the mixture will start to boil.
   2. Assess the fraction of the first bubble of vapor.

Answer 1

You will observe that in second part mole fraction of Benzene in vapour is greater than that of toluene.That means our answer is correct because molecular weight of benzene is less and thus it has higher volatility.See the detailed solution.

Toluene Assumptions :- Assurning the mixture of Benzene and behaves Ideal soln. in their liquid and vapour phases phases respectively, Also, Molecular weight of Benzene. Co to .M, = 48 kg Toluene GG Hs CH 31 M2 = 92 kg Kmot kmol (a) Given, 01282 kmoy 1 kg of of Benzene and 1 kg of Toluene are mixed. .. moles of Benzene in mixture (Liquid), nie weight Molemlar wt n = 1 а 78 kg 1 kmol similarly, moles of Toluene in mixture n2 = 1kg 92 kg lama H₂ 2.01087 kmol - :. Total moles of mixture, na nian₂ =. 01282 + .01087 . 02369 kmol Mole fraction of Benzene in the mixture, n . 8,= .5411 012 8 2 kmol 02369 kmot Also, mole fraction of Toluene, da sis .45 89 व plz= •01087 kmol 02369 kmol at Let 'p' be the pressure of the mixture which it flashes and the liquid and vapour will be in equilibrium . Let Y, and Y2 be the mole fraction of Benzene Also,

in the and Toluene vapour phase respectively. From Raoult's how I for ideal liq, solm.) o partial pressure, bi=x, psat . X2 P Sat where are [ه ۱ I we Probe are partial pressure of Benzene and Toluene in vapour phase. P, sot and Pusat vapour prenure of Benzene and Toluene respectively, AISO, pi=Y,P and þz=YzP [Dalton's adding eqni ® and get, bi+P2 = xip, sat + x2 pusat Sat » y, P+YzP xip, sot + x2 P. Sat P=xipsat +22P25 Given pisat = 53kPa , Psat = 18.5 kPa P = (05411453+ 14589x 1815 kPa P =37,168 kPa 1 AISO, ( 6 ) xip,sat bra = Y, P = x, p,sat % y, x 37.168 kPaz .5411 x 53 kPa 7,2-7715 Ye +Y₂=1 => Y221-4, l-Ya Also, [ sum of mole fraction is always i 1-7715 Ya 3.2285 वा