A liquid mixture of 25 mol% n-pentane(1), 45 mol forall n - hexane(2) and 30 mol% n-heptune(3), initially at 69C and a high pressure, is flashed by isothermal reduction of pressure to 1.013 bar. The system obeys Raoult's law. Antoine equations for the vapour pressure of pure species give the saturation pressure at 69C, as P_{1} ^ (am) = 2.721 bar, P_{2} ^ (mt) = 1.024 bar, P_{3} ^ (sst) = 0.389 bar.

(1) Show that the above system exists in vapour and liquid phases. [5marks]

(ii) Show that the mole percent of vapour is 42.6%.

(iii) Determine vapour phase composition (y).

[6 marks]

[2 marks]