Chemistry 232 Multicomponent Phase Equilibria

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

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

A Liquid-vapour Phase Diagram  composition axis: PB*PB* ZAZA PA*PA* vapour liquid

A Blow-up of the Two-phase Region  the lever rule:nl = l’n’ ZAZA l’l liquid vapour n n’ P PB*PB* PA*PA* l liq l vap

Moving Down an Isopleth  isopleth - constant total composition. ZAZA b d liquid vapour n n’ P (torr) a c e

Temperature-composition Phase Diagrams TA*TA* TB*TB* ZAZA T / K xAxA yAyA

Simple Distillation of Liquid Mixtures  Vapour at composition a’ 2 is condensed, it becomes richer in the more volatile component. TA*TA* TB*TB* ZAZA T / K a1a1 boilcondense a2a2 a’ 2 a3a3

Fractional Distillations  Repeat the evaporation and condensation cycle! TA*TA* TB*TB* ZAZA T / K a1a1 yAyA boil condense a2a2 a’ 3 a’ 2 a3a3 a4a4 a’ 4

a5a5 TA*TA* TB*TB* ZAZA T / K a1a1 boil a2a2 a4a4 T aze a3a3 e’ condense a’ 5 a6a6 a’ 2 a’ 6 Azeotropes  From the Greek - to boil unchanged. A low boiling azeotrope.

Azeotropes  A High Boiling Azeotrope TA*TA* TB*TB* ZAZA T / K a1a1 boil a’ 2 a’ 5 T aze a4a4 e’ boil condense a2a2 a3a3 a5a5

 T UC - the upper critical temperature. T / K T uc XAXA a’l ’a``l `` tie-line F`=2 F`=1 Liquid-Liquid Phase Diagrams

 T LC - the lower critical temperature. T / K F`=2 XAXA T LC a’l ’a``l `` tie-line F`=1 Liquid-Liquid Phase Diagrams

 A system exhibiting and upper and a lower critical solution temperature! T / K XAXA T LC T UC

The distillation of partially miscible liquids  Complete miscibility occurs before boiling commences. T / K ZAZA vapour 1 phase liquid 2 phase liquid L + V a1a1 a2a2 a’ 2

The distillation of partially miscible liquids  Liquids remain immiscible even up to the boiling temperature. ZAZA T / K vapour 1 phase liquid 2 phase liquid L + V bac

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,A H = enthalpy of fusion of A T A and T * A are the freezing points of the solution and pure A, respectively.

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

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

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

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. liquid solid B + solution T* B solid A + solid B solid A + solution eutectic tie line T* A