Georgia Performance Standards:

1. Georgia Performance Standards: SC6. Students will understand the effects motion of atoms and molecules in chemical and physical processes. a. Compare and contrast atomic/molecular motion in solids, liquids, gases, and plasmas. Essential Questions: How do gas, liquid, and solid molecules move? How can various intermolecular forces affect the properties of a liquid? How can phase diagrams be used to determine the changes of state in matter- How can you predict the energy requirements needed for the changes of state in matter?

2. Objectives: Liquids, Vapor Pressure & Boiling Point 1. Compare and contrast atomic/molecular motion in solids, liquids, gases, and plasmas. 2. To understand the properties of a liquid 3. To understand the relationship among vaporization, condensation and vapor pressure 4. To relate the boiling point of water to its vapor pressure

3. States of Matter The fundamental difference between states of matter is the distance between particles.

4. States of Matter Because in the solid and liquid states particles are closer together, we refer to them as condensed phases.

5. The States of Matter • The state a substance is in at a particular temperature and pressure depends on two antagonistic entities: • the kinetic energy of the particles; • the strength of the attractions between the particles.

6. Liquids • Many of the properties due to internal attraction of atoms. • Beading • Surface tension =resistance of a liquid to an increase in its surface area. • Capillary action = spontaneous rising of a polar liquid in a narrow tube. • Stronger intermolecular forces cause each of these to increase.

7. Surface Tension Surface tension results from the net inward force experienced by the molecules on the surface of a liquid.

8. Surface tension • Molecules at the the top are only pulled inside. • Molecules in the middle are attracted in all directions. • Minimizes surface area.

9. Capillary Action • Liquids spontaneously rise in a narrow tube (capillary action). • Inter molecular forces are cohesive, connecting like things (same molecule). • Water attracting other water molecules • Adhesive forces connect to something else (different molecules). • Glass is polar and it attracts water molecules.

10. Beading • If a polar substance is placed on a non-polar surface. • There are cohesive, • But no adhesive forces. • And Visa Versa

11. Viscosity • How much a liquid resists flowing. • Viscosity increases with stronger intermolecular forces and decreases with higher temperature. • Large forces, more viscous. • Large molecules can get tangled up. • EX: Water has a lower viscosity rate than syrup.

12. Viscosity • Resistance of a liquid to flow is called viscosity. • It is related to the ease with which molecules can move past each other.

13. A. Evaporation and Vapor Pressure • Vaporization or evaporation • Endothermic

14. A. Evaporation and Vapor Pressure • Vapor Pressure • Amount of liquid first decreases then becomes constant • Condensation - process by which vapor molecules convert to a liquid • When no further change is visible the opposing processes balance each other - equilibrium

15. A. Evaporation and Vapor Pressure • Vapor pressure - pressure of the vapor present at equilibrium with its liquid • Vapor pressures vary widely - relates to intermolecular forces

16. B. Boiling Point and Vapor Pressure

17. B. Boiling Point and Vapor Pressure

18. Vapor Pressure • At any temperature some molecules in a liquid have enough energy to escape. • As the temperature rises, the fraction of molecules that have enough energy to escape increases.

19. Vapor Pressure As more molecules escape the liquid, the pressure they exert increases.

20. Vapor Pressure The liquid and vapor reach a state of dynamic equilibrium: liquid molecules evaporate and vapor molecules condense at the same rate.

21. Vapor Pressure • The boiling point of a liquid is the temperature at which it’s vapor pressure equals atmospheric pressure. • The normal boiling point is the temperature at which its vapor pressure is 760 torr.

22. Performance Tasks: • Compare & contrast various intermolecular forces (dipole-dipole, hydrogen bonding and London dispersion forces). • Analyze the effect of intermolecular forces on the properties of liquids. • Evaluate the interactions among water molecules • Determine the energy requirements for the changes of state by calculate the heat of fusion and the heat of vaporization • Analyze phase change diagrams to determine the changes of state.

23. A. Intermolecular Forces • Reviewing what we know • Low density • Highly compressible • Fill container • Gases • Solids • High density • Slightly compressible • Rigid (keeps its shape)

24. A. Intermolecular Forces • Intermolecular forces – occur between molecules • Intramolecular forces – occur inside the molecules

25. Intermolecular forces • Inside molecules (intramolecular) the atoms are bonded to each other. • Intermolecular refers to the forces between the molecules. • These are what hold the molecules together in the condensed states.

26. Intermolecular forces • Strong • covalent bonding • ionic bonding • Weak • Dipole dipole • London dispersion forces • Hydrogen Bonds • During phase changes the molecules stay intact. • Energy used to overcome forces.

27. Intermolecular Forces The attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together.

28. Intermolecular Forces They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.

29. Intermolecular Forces These intermolecular forces as a group are referred to as van der Waals forces.

30. A. Intermolecular Forces • Dipole – dipole attraction

31. Dipole-Dipole Forces

32. A. Intermolecular Forces • Hydrogen Bonding • Occurs between H and highly electronegative atom (for example N, O, F)

33. A. Intermolecular Forces • Affects physical properties • Boiling point • Hydrogen Bonding

34. Hydrogen Bonding

35. A. Intermolecular Forces • Formation of instantaneous dipoles • London Dispersion Forces

36. A. Intermolecular Forces • Nonpolar molecules • London Dispersion Forces

37. A. Intermolecular Forces • Become stronger as the sizes of atoms or molecules increase • London Dispersion Forces

38. London Dispersion Forces

39. B. Water and Its Phase Changes • Heating/cooling curve

40. B. Water and Its Phase Changes • Normal boiling point – at 1 atm = 100oC • Normal freezing point – at 1 atm = 0oC • Density • Liquid water = 1.00 g/mL • Ice = 0.917 g/mL

41. Phase Changes

42. Energy Changes Associated with Changes of State The heat of fusion is the energy required to change a solid at its melting point to a liquid.

43. Energy Changes Associated with Changes of State The heat of vaporization is defined as the energy required to change a liquid at its boiling point to a gas.

44. Energy Changes Associated with Changes of State • The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other. • The temperature of the substance does not rise during a phase change.

45. C. Energy Requirements for the Changes of State • Changes of state are physical changes • No chemical bonds are broken

46. C. Energy Requirements for the Changes of State • Molar heat of fusion – energy required to melt 1 mol of a substance • Molar heat of vaporization – energy required to change 1 mol of a liquid to its vapor

47. Phase Diagrams Phase diagrams display the state of a substance at various pressures and temperatures and the places where equilibria exist between phases.

48. Phase Diagrams • The circled line is the liquid-vapor interface. • It starts at the triple point (T), the point at which all three states are in equilibrium.

49. Phase Diagrams It ends at the critical point (C); above this critical temperature and critical pressure the liquid and vapor are indistinguishable from each other.

50. Phase Diagrams Each point along this line is the boiling point of the substance at that pressure.