1. Intermolecular Forces and Liquids and Solids Chapter 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 11-1 The kinetic molecular theory of liquids and solids A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary. 2 Phases Solid phase - ice Liquid phase - water 11.1

3. 11-2 Intermolecular Forces 11.2 Intermolecular forces are attractive forces between molecules. Intramolecular forces hold atoms together in a molecule. Intermolecular vs Intramolecular 41 kJ to vaporize 1 mole of water (inter) 930 kJ to break all O-H bonds in 1 mole of water (intra) Generally, intermolecular forces are much weaker than intramolecular forces. “Measure” of intermolecular force boiling point melting point  H vap  H fus  H sub

4. Intermolecular Forces Dipole-Dipole Forces Attractive forces between polar molecules Orientation of Polar Molecules in a Solid 11.2

5. Intermolecular Forces Ion-Dipole Forces Attractive forces between an ion and a polar molecule 11.2 Ion-Dipole Interaction

6. 11.2

7. Intermolecular Forces Dispersion Forces Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules 11.2 ion-induced dipole interaction dipole-induced dipole interaction

8. Induced Dipoles Interacting With Each Other 11.2

9. Intermolecular Forces Dispersion Forces Continued 11.2 Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted. Polarizability increases with: greater number of electrons more diffuse electron cloud Dispersion forces usually increase with molar mass.

10. S O O What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH 4 CH 4 is nonpolar: dispersion forces. SO 2 SO 2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO 2 molecules. 11.2

11. Intermolecular Forces Hydrogen Bond 11.2 The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A H … B A H … A or A & B are N, O, or F

12. Hydrogen Bond 11.2

13. Why is the hydrogen bond considered a “special” dipole-dipole interaction? Decreasing molar mass Decreasing boiling point 11.2

14. Worked Example 11.1

15. Worked Example 11.2

16. 11-3 Properties of Liquids Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension 11.3

17. Pg 459

18. Figure 11.9

19. Properties of Liquids Cohesion is the intermolecular attraction between like molecules 11.3 Adhesion is an attraction between unlike molecules Adhesion Cohesion

20. Properties of Liquids Viscosity is a measure of a fluid’s resistance to flow. 11.3 Strong intermolecular forces High viscosity

21. Maximum Density 4 0 C Ice is less dense than water Density of Water 11.3 Water is a Unique Substance The structure and properties of water

22. Figure 11.11

23. Evaporation Greatest Order Least Order 11.8 Condensation T 2 > T 1 Liquid – vapor equilibrium Phase change is the transformation from one phase to another occur when energy (usually in the form of heat) is added or removed. Phase changes are physical changes characterized by changes in molecular order, molecules in the solid phase have the greatest order, and those in the gas phase have the greatest randomness. 11-8

24. The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation H 2 O (l) H 2 O (g) Rate of condensation Rate of evaporation = Dynamic Equilibrium 11.8

25. Before Evaporation At Equilibrium 11.8

26. Molar heat of vaporization (  H vap ) is the energy required to vaporize 1 mole of a liquid at its boiling point. The molar heat of vaporization is directly related to the strength of intermolecular forces that exist in the liquid. ln P = -  H vap RT + C Clausius-Clapeyron Equation P = (equilibrium) vapor pressure T = temperature (K) R = gas constant (8.314 J/K mol) 11.8 Vapor Pressure Versus Temperature

27. Worked Example 11.7

28. The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm. 11.8

29. The critical temperature (T c ) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. The critical pressure (P c ) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature. 11.8

30. The Critical Phenomenon of SF 6 T < T c T > T c T ~ T c T < T c 11.8

31. Melting 11.8 Freezing H 2 O (s) H 2 O (l) The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium Liquid – solid equilibrium

32. Molar heat of fusion (  H fus ) is the energy required to melt 1 mole of a solid substance at its freezing point. 11.8

33. Heating Curve

34. Sublimation 11.8 Deposition H 2 O (s) H 2 O (g) Molar heat of sublimation (  H sub ) is the energy required to sublime 1 mole of a solid.  H sub =  H fus +  H vap ( Hess’s Law) Solid – vapor equilibrium

35. A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. Phase Diagram of Water 11.9 11-9 phase diagram

36. 11.9 Phase Diagram of Carbon Dioxide At 1 atm CO 2 (s) CO 2 (g)

37. 11.9 Effect of Increase in Pressure on the Melting Point of Ice and the Boiling Point of Water Boiling point of water decreases with decreasing pressure so its hard to boiling an egg on a mountain top because the amount of heat delivered to the egg is not enough for cooking. Why is the food in the pressure cookers will be cook faster? The melting point of ice decreases with increasing external pressure. This phenomenon helps to make ice skating possible.

38. Chemistry In Action: Liquid Crystals