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Chemistry 232

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

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Chemistry 232

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  1. Chemistry 232 Multicomponent Phase Equilibria

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

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

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

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

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

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

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

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

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

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

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

  16. The distillation of partially miscible liquids • Liquids remain immiscible even up to the boiling temperature. vapour L + V T / K L + V a b c 1 phase liquid 2 phase liquid 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 • For a solution of B in liquid A. T*A T/K liquid solid liquidus curve XA

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

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

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

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