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Chemistry 232

Chemistry 232. Multicomponent Phase Equilibria. Raoult’s Law . P A *. liquid. vapour. P B *. X A. Variation in the total vapour pressure of a two component liquid mixture according to Raoult’s Law . The Variation in Terms of Gas Phase Mole Fractions. P A *. liquid. vapour. P B *. y A.

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Chemistry 232

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  1. Chemistry 232 Multicomponent Phase Equilibria

  2. Raoult’s Law PA* liquid vapour PB* XA Variation in the total vapour pressure of a two component liquid mixture according to Raoult’s Law

  3. The Variation in Terms of Gas Phase Mole Fractions PA* liquid vapour PB* yA yA the vapour phase mole fraction of A.

  4. A Liquid-vapour Phase Diagram liquid PA* vapour PB* ZA composition axis:

  5. A Blow-up of the Two-phase Region

  6. Moving Down an Isopleth 450 liquid a 350 P (torr) b c l’ n 300 n’ l d 250 vapour e 200 0.0 0.25 0.75 1.00 0.50 • isopleth - constant total composition • lever rule: nl = l’n’ ZA

  7. Temperature-composition Phase Diagrams TB* T / K xA yA ZA TA*

  8. Simple Distillation of Liquid Mixtures TB* a’2 T / K a2 boil condense a1 TA* a3 ZA Vapour at composition a’2 is condensed, it becomes richer in the more volatile component.

  9. Fractional Distillations Repeat the evaporation and condensation cycle!

  10. Azeotropes • A low boiling azeotrope.

  11. Azeotropes A High Boiling Azeotrope

  12. Liquid-Liquid Phase Diagrams Tuc T / K F`=2 F`=1 tie-line a’ l ’ l `` a`` XA TUC - the upper critical temperature.

  13. Liquid-Liquid Phase Diagrams T / K F`=2 a’ l ’ l `` a`` F`=1 tie-line TLC XA TLC - the lower critical temperature.

  14. Liquid-Liquid Phase Diagrams TUC T / K TLC XA A system exhibiting and upper and a lower critical solution temperature!

  15. The distillation of partially miscible liquids vapour T / K L + V a’2 L + V a2 1 phase liquid 2 phase liquid a1 Complete miscibility occurs before boiling commences. ZA

  16. The distillation of partially miscible liquids vapour L + V T / K L + V a b c 1 phase liquid 2 phase liquid Liquids remain immiscible even up to the boiling temperature. ZA

  17. Liquid-Solid Phase Diagrams • Freezing points of solutions are dependent on the compositions of the solutions! • We have already examined briefly the freezing point depression of dilute soutions. • where fus,AH = enthalpy of fusion of A • TA and T*A are the freezing points of the solution and pure A, respectively.

  18. The Liquidus Curve for B in A T*A T/K liquid solid liquidus curve XA For a solution of B in liquid A.

  19. The Liquidus Curve for A in B T*B liquidus curve T/K liquid solid XA For a solution of A in liquid B.

  20. The S-L Phase Diagram liquid T*A eutectic T*B solid A + solution solid B + solution solid A + solid B Overlapping the curves leads to the liquid-solid phase diagram for A and B.

  21. A Blow-up of the Two-phase Region T*A liquid T*B tie line eutectic solid A + solution solid B + solution solid A + solid B Tie lines connect the liquid phase of specified composition in equilibrium with either solid A or B.

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