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20 B Week III Chapters 10 and 11

• Chapter 10, 11( except 11.4 and and 11.6 -7) • Intermolecular potentials. Dipole – Dipole, Hydrogen bonding and ion-dipole, ion-ion • Co-existence Curves, Triple point, Critical point

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20 B Week III Chapters 10 and 11

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  1. • Chapter 10, 11( except 11.4 and and 11.6 -7) • Intermolecular potentials. Dipole – Dipole, Hydrogen bonding and ion-dipole, ion-ion • Co-existence Curves, Triple point, Critical point • Solutions. Interactions in solution, Boiling Point Elevation, Freezing Point Depression and Osmotic Pressure, Electrolyte solutions Midterm next Friday: Chaps 9(no 9.7), 10, 11.-11.3 One side of page notes, closed book Review Session Wednesday 2-3 pm, in FRANZ 1178 20 B Week III Chapters 10 and 11

  2. The Rate of evaporation vs time as the vapor pressure approaches Equilibrium Evaporation rate equals the condensation Rate C2H4(l)  C2H4(g) Evaporation  Equilibrium P,V and T well defined All the Macroscopic Properties, P, V, and T are only defined at Equilibrium. Which means PV=nRT and the vdW Eq. can only be use under Equilibrium conditions Fig. 10-16, p. 459

  3. Equilibrium H2O P-T Phase Diagram

  4. H2O P-T Phase Diagram Equilibrium Vapor Pressure Super heated H2O liquid Will spontaneously vaporize Super cooled H2O liquid will Spontaneously freeze In both spontaneous processes the system will go to the Equilibrium State (Phase) and Pressure Table 10-3, p. 460

  5. P NP NP NP P NP NP P NP P P H-b vdW B-di vdW di-di B-dipole vdW di-die vdW di-di H-b P(polar), NP 9non-polar), H-b(hydrogen bonds), B-di(bond-dipole) di-di(dipole-dipole), vdW(van der Waals P=[nRT/(V– nb)] – [a(n/V)2] n=N/NA and R=Nak Notice the difference between polar(P) molecules (dipole moment ≠0) and non-polar(NP) molecules (no net dipole moment =0) CO2 and CH4

  6. Polar Non-polar Non-polar Bond dipoles Hydrogen-bonding Bond dipoles dipole-dipole

  7. Boiling points for pure liquids Boiling Point reflects bond strengths (e~ Ze) Or Ze Fig. 10-12, p. 456

  8. Equilibrium Vapor Pressure vs Temperature for SP3 bonded molecules(pure-liqs) Of the form R2O, R=H, CH3, C2H5 and C6H5. Except for C6H5 with the large Pi-ring of the phenyl group all have lower boiling point than water, so none of these molecules are H-bonded, they are dispersion bonded through the Hydrocarbon groups and and dipole bonded through R2O dipole. Solids Room Temp P P P NP Fig. 10-17, p. 460

  9. Chemical bonds versus Physical bonds CH groups in the R-O-R compounds, many such interactions can add to substantial Physical bonds Uses Van der Waals Eq dipole-dipole of the R-O-R compounds Chemical bonds Do not use Van der Waal’s Eq Why?

  10. H2O(l) Density of H2O vs Temperature Not @ Equilibrium H2O(s) As T decreases the <R> decreases and therefore the density increases. The phase Transition occurs at the highest Density H2O(l) Fig. 10-15, p. 458

  11. H2O P-T Phase Diagram Equilibrium Vapor Pressure Super heated H2O liquid Will spontaneously vaporize Super cooled H2O liquid will Spontaneously freeze In both spontaneous processes the system will go to the Equilibrium State (Phase) and Pressure Table 10-3, p. 460

  12. e In Solutions, for example when NaCl(s) is dissolved in H2O(l). + H2O Dissolution of a polar solid by a polar solid by a polar liquid A non-polar liquid e.g., benzene, would not dissolve NaCl? NaCl(s) + H2O(l) Na+(aq) +Cl-(aq) (aq) means an aqueous solution, where water is the solvent, major component. The solute is NaCl, which is dissolved, minor component Water molecules solvates the ions the Cation (Na+) and the Anion (Cl-). The forces at play here are Ion dipole forces Fig. 10-6, p. 450

  13. -2∂ First Solvation Shell of the Solvent -2∂ +∂ -2∂ + -2∂ +∂ +∂ Solvated Na+ Fig. 10-6a, p. 450

  14. Dissolution of K2SO4 in water 2nd solvation shell Fig. 11-3, p. 480

  15. In a solution of solvent A and solute B, the important thermodynamic variables are V, T, molar Concentration of [A] and [B] and the relative composition X The Molarity moles of B/ Liters of Solution [A]=nA/Vsol and [B]=nB/Vsol in units of mols L-1 The composition in mole fraction: XA= nA/(nA + nB) and XB= nB/(nA + nB) XA + XB =1 and XA=1 -XB Because Volume depends on the Temperature, the Molarity is not always the Best variable, the Molality {B} = Moles of Solute/ kg of Solvent mol kg-1 {B}= nB//kg of solvent, since the density of water is defined as kg/L

  16. In acid base reactions for example: HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) HCl is the Acid and H2O is the Base or NaOH(s)  Na+(aq) + OH-(aq) Where OH-, the hydroxide ion is the base The Neutralization reaction 2H2O(l)  H3O+(aq) + OH-(aq)

  17. -e +e Electro-negativity of atoms Dipole moment =eRe A measure of the charge separation In a molecule the more Electronegative atom in a bond will transfer electron density from the less Electronegative atom This forms dipole along the bond

  18. -e Dipole-Dipole interaction +e Strongest of the physical bonds Except for hydrogen bonds Which are the strongest of the Physical bonds, e.g., (H2O)2 dimer Dipole moment =eRe

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