1. CHE1102, Chapter 11 Learn, 1 Chapter 11 Intermolecular Attractions and the Properties of Liquids and Solids Practice Exercises 11.1-3, 8- 9, 11, 13-14, 16 Examples: 11.1-4, 6 In Text Problems

2. CHE1102, Chapter 11 Learn, 2 The States of Matter

3. CHE1102, Chapter 11 Learn, 3 The States of Matter

4. CHE1102, Chapter 11 Learn, 4 – What is happening on the molecular level that causes a solid to be a solid ? – What is happening on the molecular level that causes a liquid to be a liquid ? – What is happening on the molecular level that causes a gas to be a gas ? Intermolecular Forces The attractive forces between molecules

5. CHE1102, Chapter 11 Learn, 5 Intermolecular Forces The attractions between molecules are not nearly as strong as the intramolecular attractions (bonds) that hold compounds together. Many physical properties reflect intermolecular forces, like boiling points, melting points, viscosity, surface tension, and capillary action.

6. CHE1102, Chapter 11 Learn, 6 Types of Intermolecular Forces Weakest to strongest forces:  dispersion forces (or London dispersion forces)  dipole–dipole forces  hydrogen bonding (a special dipole–dipole force)  ion–dipole forces o Note: The first two types are also referred to collectively as van der Waals forces.

7. CHE1102, Chapter 11 Learn, 7 Types of Intermolecular forces 1. Dipole - Dipole – the attractive forces between polar molecules ++ -- Br-Cl is a polar molecule with a permanent dipole moment

8. CHE1102, Chapter 11 Learn, 8 Since unlike charges attract, polar molecules are attracted to each other on the molecular level dipole-dipole IM attractive force Dipole-Dipole Forces

9. CHE1102, Chapter 11 Learn, 9 Dipole-dipole interactions cause molecules to orient to maximize attractive forces between molecules Molecules line up and assume a somewhat “ordered” state Dipole-Dipole Forces

10. CHE1102, Chapter 11 Learn, 10 The quantitative measure of the extent of intermolecular forces is reflected in the molecules melting point or boiling point ! solid at 25  C A liquid at 25  C B Which possesses a greater degree of order ? A Substance A exhibits more IM attractive forces vs. B MP of A > 25  C while MP of B < 25  C

11. CHE1102, Chapter 11 Learn, 11 The higher the boiling point, the more order the substance exhibits …..(in other words)…. The higher the boiling point, the greater the extent of the intermolecular forces between molecules Dipole-Dipole Forces

12. CHE1102, Chapter 11 Learn, 12 2. London dispersion forces – the very short lived attractive forces caused by the instantaneous displacement of electrons Fritz London 1900 – 1954 Types of Intermolecular forces

13. CHE1102, Chapter 11 Learn, 13 Electron cloud momentarily distorts to give rise to non-symmetric electron cloud producing an instantaneous dipole

14. CHE1102, Chapter 11 Learn, 14 Instantaneous dipole – distorted electrons give rise to a temporary dipole Instantaneous dipoles provide some additional intermolecular ordering on the molecular level before instantaneous dipoles: He nonpolar instantaneous dipoles occurring: He slightly polar

15. CHE1102, Chapter 11 Learn, 15 Extent of London dispersion is determined by MW London dispersion forces increase as MW increases London Dispersion Forces

16. CHE1102, Chapter 11 Learn, 16 Arrange the following in order of increasing boiling points; C 3 H 8, CH 4, C 8 H 18

17. CHE1102, Chapter 11 Learn, 17 Arrange the following in order of increasing boiling point: F 2, H 2 S

18. CHE1102, Chapter 11 Learn, 18 Factors Which Affect Amount of Dispersion Force in a Molecule number of electrons in an atom (more electrons, more dispersion force) size of atom or molecule/molecular weight shape of molecules with similar masses (more compact, less dispersion force)

19. CHE1102, Chapter 11 Learn, 19 Which Have a Greater Effect: Dipole–Dipole Interactions or Dispersion Forces? If two molecules are of comparable size and shape, dipole–dipole interactions will likely be the dominating force. If one molecule is much larger than another, dispersion forces will likely determine its physical properties.

20. CHE1102, Chapter 11 Learn, 20 Types of Intermolecular Forces 3. Hydrogen Bonding – occurs between polar molecules that contain a hydrogen atom that is attached to a F, or O, or N “H–F” or “H–O” or “H–N” H-bonding is an unusually strong dipole- dipole that provides more order on the molecular level than a routine dipole-dipole

21. CHE1102, Chapter 11 Learn, 21

22. CHE1102, Chapter 11 Learn, 22 H-bonding is responsible for holding the two strands of DNA together!

23. CHE1102, Chapter 11 Learn, 23 H-bonding gives rise to the “open structure” of ice, thus H 2 O (s) is less dense than H 2 O ( ) and thus, ice floats

24. CHE1102, Chapter 11 Learn, 24 London dispersion forces are present in all substances and increase with increasing MW H-bonding > dipole-dipole

25. CHE1102, Chapter 11 Learn, 25 Arrange the following in order of increasing boiling point; Kr, H 2 S, NaCl, Ne, NH 3, F 2

26. CHE1102, Chapter 11 Learn, 26 Liquid Properties Affected by Intermolecular Forces boiling point (previously discussed) and melting point viscosity surface tension capillary action

27. CHE1102, Chapter 11 Learn, 27 Viscosity Resistance of a liquid to flow is called viscosity. The greater the viscosity, the slower a liquid flows. Viscosity increases with stronger intermolecular forces and decreases with higher temperature.

28. CHE1102, Chapter 11 Learn, 28 Which species has the greater viscosity ? C 6 H 14 ( ) or CH 3 CH 2 CH 2 CH 2 CH 2 OH ( )

29. CHE1102, Chapter 11 Learn, 29 Which species is more viscous (the greater viscosity) ? CH 3 OH ( ) at 15  C or CH 3 OH ( ) at 45  C

30. CHE1102, Chapter 11 Learn, 30 Surface Tension – the characteristic “skin” a liquid’s surface develops Surface tension increases with increasing intermolecular attractive forces Surface tension decreases with increasing temperature

31. CHE1102, Chapter 11 Learn, 31 Which species has the greater surface tension ? H 2 O ( ) at 15  C or H 2 O ( ) at 45  C

32. CHE1102, Chapter 11 Learn, 32 Which species has the greater surface tension 25  C ? CH 3 CH 2 CH 2 OH ( ) or HOCH 2 CH 2 OH ( )

33. CHE1102, Chapter 11 Learn, 33 Phase Changes

34. CHE1102, Chapter 11 Learn, 34 Energy Change & Change of State The heat of fusion is the energy required to change a solid at its melting point to a liquid. The heat of vaporization is the energy required to change a liquid at its boiling point to a gas. The heat of sublimation is the energy required to change a solid directly to a gas.

35. CHE1102, Chapter 11 Learn, 35 – the partial pressure vapor molecules exert at equilibrium liquid h h = height of the Hg = vapor pressure, VP VP water = 17.5 mm Hg VP methanol = 46.0 mm Hg at 20  C Vapor Pressure

36. CHE1102, Chapter 11 Learn, 36 VP H 2 O < VP CH 3 OH VP increases as intermolecular forces decrease VP increases as temperature increases Which species has the higher vapor pressure at 25  C ? CH 3 CH 2 CH 2 OH ( ) or HOCH 2 CH 2 OH ( ) Higher VP

37. CHE1102, Chapter 11 Learn, 37 Heating Curves

38. CHE1102, Chapter 11 Learn, 38 Heating Curve of a Solid As you heat a solid, its temperature increases linearly until it reaches the melting point. –q = mass × s ×  T Once the temperature reaches the melting point, all the added heat goes into melting the solid. –The temperature stays constant. Once all the solid has been turned into liquid, the temperature can again start to rise. –Ice/water will always have a temperature of 0 °C at 1 atm.

39. CHE1102, Chapter 11 Learn, 39 Heat of Fusion The amount of heat energy required to melt one mole of the solid is called the heat of fusion,  H fus. –Sometimes called the enthalpy of fusion It is always endothermic; therefore,  H fus is +.   H crystallization = −  H fusion  Generally much less than  H vap   H sublimation =  H fusion +  H vaporization

40. CHE1102, Chapter 11 Learn, 40 Heating Curve of a Liquid As you heat a liquid, its temperature increases linearly until it reaches the boiling point. –q = mass × s ×  T Once the temperature reaches the boiling point, all the added heat goes into boiling the liquid; the temperature stays constant. Once all the liquid has been turned into gas, the temperature can again start to rise.

41. CHE1102, Chapter 11 Learn, 41 Heat of Vaporization The amount of heat energy required to vaporize one mole of the liquid is called the heat of vaporization,  H vap. –Sometimes called the enthalpy of vaporization It is always endothermic; therefore,  H vap is +.   H condensation = −  H vaporization

42. CHE1102, Chapter 11 Learn, 42 Heating Curve of Water Assume 1 mol H 2 O – how much heat is involved in this process?

43. CHE1102, Chapter 11 Learn, 43 Segment 1 Heating 1.00 mole of ice at −25.0 °C up to the melting point, 0.0 °C q = mass × s ×  T –Mass of 1.00 mole of ice = 18.0 g –s (ice) = 2.09 J/g ∙ °C

44. CHE1102, Chapter 11 Learn, 44 Segment 2 Melting 1.00 mole of ice at the melting point, 0.0 °C q = n ∙  H fus – n = 1.00 mole of ice –  H fus = 6.02 kJ/mol

45. CHE1102, Chapter 11 Learn, 45 Segment 3 Heating 1.00 mole of water at 0.0 °C up to the boiling point, 100.0 °C q = mass × s ×  T –Mass of 1.00 mole of water = 18.0 g –s (water) = 4.18 J/g∙ °C

46. CHE1102, Chapter 11 Learn, 46 Segment 4 Boiling 1.00 mole of water at the boiling point, 100.0 °C q = n ∙  H vap – n = 1.00 mole of ice –  H vap = 40.7 kJ/mol

47. CHE1102, Chapter 11 Learn, 47 Segment 5 Heating 1.00 mole of steam at 100.0 °C up to 125.0 °C q = mass × s ×  T –Mass of 1.00 mole of water = 18.0 g –s (steam) = 2.01 J/g ∙ °C

48. CHE1102, Chapter 11 Learn, 48 Summation of All Segments Heating 1.00 mole of ice at -25.0 °C up to 125.0 °C q = 0.941 kJ + 6.02 kJ + 7.52 kJ + 40.7 kJ + 0.904 kJ = 56.085 kJ

49. CHE1102, Chapter 11 Learn, 49 – temperature where the vapor pressure of the liquid is equal to the applied pressure normal BP – temp of the boiling point at 1 atm Boiling Point

50. CHE1102, Chapter 11 Learn, 50 pressure cooker

51. CHE1102, Chapter 11 Learn, 51 Supercritical Fluids Gases liquefy when pressure is applied. The temperature beyond which a gas cannot be compressed to form a liquid is called its critical temperature. The pressure at which a gas at its critical temperature is converted to a liquid is called its critical pressure. The state beyond this temperature is called a supercritical fluid.

52. CHE1102, Chapter 11 Learn, 52 Phase Diagrams – graphs of pressure and temperature phase changes

53. CHE1102, Chapter 11 Learn, 53 line AD represents melting or freezing point of substance line AB represents boiling point of substance line AC represents sublimation of substance

54. CHE1102, Chapter 11 Learn, 54 how does water exist at 100  C and 5 atm ? liquid how does water exist at 100  C and 0.5 atm ? gas can you boil water at 50  C ? yes can you boil water at -5  C ? no can ice exist at + 2  C ? no

55. CHE1102, Chapter 11 Learn, 55 How do you make a snowball ? What is happening at point A ? triple point – all three phases coexist together

56. CHE1102, Chapter 11 Learn, 56 How does CO 2 exist at -40  C and 7 atm ? liquid What temp does CO 2 boil ? depends Can CO 2 melt at 4 atm ? doesn’t have one What is the normal BP ? No What is the triple point ? -56.4  C, 5.11 atm What is happening at point Z ?

57. CHE1102, Chapter 11 Learn, 57 critical point – no distinct difference between liquid and gas states at temperature and pressure above this point supercritical fluid – a state that is in between a liquid and gas phase

58. CHE1102, Chapter 11 Learn, 58

59. CHE1102, Chapter 11 Learn, 59

60. CHE1102, Chapter 11 Learn, 60 Green coffee beans are immersed in supercritical CO 2 at 90  C and about 180 atm. The caffeine dissolves into the CO 2 supercritical fluid and is extracted and removed