1. Phases of Matter Overview Solid, liquid, gas (vapor) properties
Molecular motion vs. phase
Gases and pressure
Liquids, evaporation, boiling
Solids, melting

2. Properties of the different phases
1-1. In your group, list the different physical properties of
Solids
Liquids
Gases or vapors

3. Solids Fixed volume and shape Heating  melting
Powders vs. chunk of something
Crystals

4. Liquids Fixed volume, but adopt shape of container “Wet”, pourable
Heating  vaporization (boiling)
Cooling  freezing

5. Gases or Vapors
No fixed volume or shape, assume shape and volume of container
Cooling  condensation

6. What is the difference at the molecular level?
Molecules are always in motion: kinetic energy
Molecules are attracted to each other (intermolecular forces)
Amount of motion related to substance and temperature
Solid
Atoms/molecules very close to each other in crystal lattice
Fixed positions relative to each other
Molecular motion: vibrational only

7. Crystal Lattice—NaCl

8. Crystal Lattice

9. Crystal lattice of molecular solid

10. Water crystal lattice

11. Energy and Molecules Energy and phases of matter
Molecules are always in motion: kinetic energy
Amount of motion related to temperature
Solid: crystal lattice, molecular motion is predominantly vibrational
Liquid: molecules in close proximity, molecular motion is vibrational, rotational, translational

12. Liquids Rotational motion: molecules can rotate in space (spinning)
Translational motion: molecules move relative to each other

13. Liquids
Molecules are close together (attractive forces) but have a lot of freedom of movement. Gives rise to macroscopic properties associated with liquids:
Can pour a liquid,
Adopts shape of container
Viscosity: resistance to flow

14. Energy and Molecules Energy and phases of matter
Molecules are always in motion: kinetic energy
Amount of motion related to temperature
Solid: crystal lattice, molecular motion is predominantly vibrational
Liquid: molecules in close proximity, molecular motion is vibrational, rotational, translational
Gas: molecules widely separated, translational motion predominates

15. Gas or Vapor Phase Molecules are far apart; no intermolecular forces
Molecules move independently of each other, shape and volume of container
Translational motion predominates
Elastic collisions w/ other gas molecules and with container walls
Collisions with container walls gives rise to “pressure”

16. Phase Changes
Molecular motion (Kinetic Energy, KE) increases with temperature:
KE  Tabs (Kelvin scale)
KE = ½ mv2
m = mass, v = velocity
(Kinetic Molecular Theory)

17. Phase Changes: Solid  Liquid
Solid: vibrational motion increases with temperature until energy overcomes intermolecular forces to some extent.
Lattice collapses but molecules still in close proximity.
More molecular motion possible (rotational, translational)
Liquid ensues
MELTING

18. Phase Changes: Liquid  Gas
Liquid: motion (vibrational, rotational, translational) increases with temperature.
Molecules eventually have enough kinetic energy to completely overcome intermolecular forces.
Molecule escape into gas phase.
VAPORIZATION

19. Phase Changes: Gas  Liquid
Vapor: motion (translational) decreases with decreasing temperature.
Molecules eventually do not have enough kinetic energy to overcome intermolecular forces; stick together on collisions.
Molecules cluster and form droplets of liquid.
CONDENSATION (precipitation)

20. Phase Changes: Liquid  Solid
Liquid: motion (vibrational, rotational, translational) decreases with decreasing temperature.
Molecules stick together more and more as substance is cooled. Eventually form small crystal lattices (seed crystals, nucleation) which grow.
FREEZING

21. Other Phase Changes
Solid  Vapor: sublimation (low temperature, low pressure)
“dry” ice, frozen CO2
snow disappearing below freezing temps
Vapor  Solid: deposition (low temperature, low pressure)
frost

23. Phase Changes gas liquid solid vaporization condensation sublimation
deposition
Energy of system
liquid
freezing
melting
solid

24. Heating Curve Water vapor Liquid water & vapor (vaporization)
100
Temperature, ºC
Liquid water 75 50 25
Ice & liquid water melting
–25
ice
Heat added (kJ)

25. Properties of Gases (Gas Laws)
Pressure and Temperature are directly proportional
Pressure and volume are inversely proportional
Volume and temperature are directly proportional (video)
Volume and amount of a gas are directly proportional
What is happening at the molecular level?

26. Pressure (P) and Temperature (T)
Pressure results from collisions of molecules w/ container walls.
As temperature (T) , molecules move faster (more KE), more collisions, P 
T  then P 
T  then P 
Directly proportional
Assumes constant volume

27. Pressure (P) and Volume (V)
Pressure results from collisions of molecules w/ container walls.
As Volume (V) , number of collisions decreases, P 
V  then P 
V  then P 
Inversely proportional
Assumes constant temperature

28. Volume (V) and Temperature (T)
As T increases, molecules move faster.
To maintain same pressure, number of collisions must remain the same, thus V increases
T  then V 
T  then V 
Directly proportional
Assumes constant pressure

29. Volume (V) and Number of molecules
Two samples of gas at the same P, T, and V:
same number of collisions
same number of molecules

30. Properties of Gases Explain each of the following:
Balloons hung outside in the sunshine pop.
A hot air balloon rises up in the air.
Collapsing can.
Balloon in liquid nitrogen (video).
Your water bottle shrinks when you fly to Dallas.
How you pull liquid up in a straw.
How a siphon works.

31. Gas Laws—Quantitative
Pressure and Temperature are directly proportional: P = C1 x T
Pressure and volume are inversely proportional:
Volume and Temperature are directly proportional: V = C3 x T
Volume and amount are directly proportional: V = C4 x n

32. Gas Laws—Quantitative
V = C3 x T
V = C4 x n
P = C1 x T
P x V = n x R x T
Ideal Gas Equation (Law)

33. Molecular Effusion and Diffusion
ACTIVITY: smelly balloons
perfume

34. Molecular Effusion and Diffusion
perfume

35. Molecular Effusion and Diffusion
perfume

36. Molecular Effusion and Diffusion
perfume

37. Molecular Effusion and Diffusion
Effusion & Diffusion are dependent upon:
Temperature (hotter = faster)
Molecular Size (bigger = slower)

38. Properties of Liquids Intermolecular attractive forces (IMAF)
Forces between molecules
“Like dissolves like.”  similar IMAF
Stronger forces
Larger molecules
Polar molecules (like water)

39. Properties of Liquids Viscosity: resistance to flow Surface Tension
As IMAF  viscosity 
Viscosity  as T 
Surface Tension
Surface effect of stronger IMAF
As IMAF  surface tension 
Surface tension  as T 
Surfactants

40. Vapor Pressure
Vapor pressure: the pressure exerted by the vapor above a liquid when the liquid and the vapor are in dynamic equilibrium
VERY difficult conceptually for students

41. Vapor Pressure Pvap Dynamic equilibrium:
molecules  vapor = molecules  liquid
Molecules escape into vapor phase

42. Vapor Pressure Pvap  as T  When Pvap = Patm: “boiling”
Bubbles of gas in liquid

43. Explain the following…
How a pressure cooker works.
Why it takes longer to cook rice or pasta at high altitude.
How we were able to boil water with ice.

44. Heating Curve Water vapor Liquid water & vapor (vaporization)
100
Temperature, ºC
Liquid water 75 50 25
Ice & liquid water melting
–25
ice
Heat added (kJ)

45. Phase Diagrams Melting Freezing solid Critical point liquid Pressure
Vaporization
Condensation
Pressure
Sublimation
Deposition
gas
Triple point
Temperature

46. Phase Diagrams solid liquid 1 atm Pressure gas Temperature
Normal melting point
Normal boiling point

47. Phase Diagrams
solid
liquid
Pressure
CO2
1 atm
gas
Temperature

48. Phase Diagrams
H2O
solid
liquid
1 atm
gas
Pressure
Temperature