1 / 25

Chem 300 - Ch 24/#1 Today’s To Do List

Chem 300 - Ch 24/#1 Today’s To Do List. Raoult’s Law & The Ideal Solution Nonideal Solutions Why do Liquid-Liquid solutions do this?? Gibbs tells all Partial Molar Quantities Gibbs-Duhem Equation. Liquid-Liquid Solutions. Both solution components are liquids Miscible in all proportions

jonah-henson
Download Presentation

Chem 300 - Ch 24/#1 Today’s To Do List

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chem 300 - Ch 24/#1 Today’s To Do List • Raoult’s Law & The Ideal Solution • Nonideal Solutions • Why do Liquid-Liquid solutions do this?? • Gibbs tells all • Partial Molar Quantities • Gibbs-Duhem Equation

  2. Liquid-Liquid Solutions • Both solution components are liquids • Miscible in all proportions • Composition in MF (xi) of liq. mixture • Both have vapor pressures • Dalton’s Law holds: • Ptotal = P1 + P2 • P1 & P2 are partial pressures • Pi = Yi Ptotal Yi = MF of i in vapor

  3. Solution Properties • Vsoln = V1 + V2 ?? Maybe…not • DHmixing = +, - , 0 ?? • Properties proportional to concentration (xi)…not always.

  4. Compare with gas mixtures • Gas: molecules far apart • Liquid: molecules close together • Gas: Attractive/repulsive forces largely ignored • Liquid: Attr/repuls forces significant • Gas: ideal gas model • Liquid: ideal solution model

  5. Raoult’s Law • P*i vapor pressure of pure i. • Pi partial pressure of i in solution of mol fract. Xi. • Raoult’s law: • Pi = P*i Xii = 1 or 2

  6. Ideal Soln: Ptotal vs Xbenz Pi = P*i Xi

  7. Neg. Devia. From RL: Cl3CH/Acetone

  8. Positive Devia. From RL: CS2/(CH3O)2CH2

  9. Pos. Devia. as fcn of Alcohol chain length (alc/H2O mixt.) 1-prop methanol

  10. Dalton’s Law & Ideal Solns • Dalton: Ptotal = P1 + P2 • Apply Raoult’s Law: • Ptotal = P*1 X1 + P*2 X2 = P*1 X1 + P*2 (1 – X1 ) = P*2 + (P*2 - P*1) X1

  11. NonIdeal Solutions • For Nonideal gases: • Introduced fugacity (f) • For Nonideal solutions: • Introduce activity (a) • Generalized Raoult’s Law: • Pi = P*i ai (a = gX)

  12. Limiting Behavior

  13. Ideal Solution

  14. The Model • Ideal Solution: • Strong Intermolecular Attractive forces • But all forces Equal: A-AB-BA-B • NonIdeal Solution: • Attractive forces NOT equal: • A-A, B-B > A-B Positive Devia from RL • A-A, B-B < A-B Negative Devia from RL

  15. Volume Nonadditivity: Partial Molar Volumes • Mixing of Ideal Solutions: • Vtotal = n1 Vm(1) + n2 Vm(2) • Nonideal Solutions: • Define a Partial Molar Volume: • Vj = (Vtotal/nj)P,T,n’ • Vtotal = n1 V1 + n2 V2

  16. Partial Molar Volumes as function of Mol fraction Note opposite effects

  17. PMV of H2O & Ethanol @ 25 ºC

  18. Gibbs-Duhem Equation • Gtotal = n1m1 + n2 m2 • mj = (G/ nj)P,T,n’ • dG = m1 dn1 + n1 dm1 + m2 dn2 + n2 dm2 • dG = -SdT + VdP + m1 dn1 + m2 dn2 • At const T, P  dG = m1 dn1 + m2 dn2 nnn • n1 dm1 + n2 dm2 = 0Gibbs-Duhem Eq.

  19. So… • n1dm1 + n2 dm2 = 0Gibbs-Duhem Eq. • Ties together the behavior of the components in a Solution.

  20. PMV of H2O & Ethanol @ 25 ºC

  21. Next Time More Applications of G-D Eq. Critical behavior in L-L solutions Activity Henry’s Law

  22. Plot of P1 = x1P*1exp[ax22+ bx32]

  23. Solution & Distillation

  24. Fractional Distillation

  25. Azeotropes

More Related