1. I. Phases Defined and Characterized
Unit 6: Phases
I. Phases Defined and Characterized

2. a. Substances vs. Mixtures
Substances = element/compound
Mixture = various combinations
b. Solids
Properties:
Low temperature
Low Kinetic energy
Slow diffusion rates
Strong intermolecular forces
Fixed volume and shape

3. c. Liquids Properties: Low to medium low temperature (KE)
Medium to slow diffusion rates
Somewhat strong IMF’s
Volume fixed
shape depends on container

4. d. Gas High KE Low attractive forces between molecules
No definite shape or volume; depends upon container
Particles spaced far, far apart

5. Phases Summary Chart Solids Liquids Gases Energy Entropy [disorder]
Shape,
Properties

6. “Heating and Cooling Curves”
Introducing…..
“Heating and Cooling Curves”
A short video by Mark Rosengarten:

7. II. Heating and Cooling Curves

8. Phase Changes
Phase Change = changing the state of a substance by altering the temperature and pressure; reversible PHYSICAL CHANGE
Dynamic Equilibrium exists when 2 phases exist together; at temperature and pressure of the phase change

9. Terms for Phase Changes
Evaporation or Vaporization
Condensation
Fusion
Solidification
Sublimation
6) Deposition

10. Concepts for Phase Changes
Energy absorbed to change from lower temp to higher temp substance
Energy released to change from a higher temp to a lower temp
Relate phase changes and terms to Heating/Cooling Curves!
Identify:
Single Phases
vs.
Dynamic Equilibrium [phase change]

11. PE vs KE Changes on Heating/Cooling Curves
Changes in KE occur whenever there is a change in TEMPERATURE
Sections with only 1 phase have KE changes
Ex.]
Changes in PE occur during a phase change when the temperature is CONSTANT
Phase changes occur on flat sections
Ex.]

12. Heat of Fusion Equation… Heat of Fusion
The amount of heat energy required to convert a substance from a solid into a liquid, or vice versa
For water: Hf = 334 J/g
Equation…

13. Heat of Vaporization Equation… Heat of Vaporization
the amount of heat energy required to convert a substance from a liquid into a gas, or vice versa
For water:
Hv = 2260 J/g
Equation…

14. Relate Hv and Hf to IMF’s
Stronger IMF’s lead to:
Higher boiling points
Lower vapor pressure
Weaker IMF’s lead to:
Low boiling points
Higher vapor pressure

15. IV. Heat Calculations
Three equations are used to calculate heat energy transferred during a heatins/cooling curve:
q = mcΔT used during…?
q = mHv used during….?
q = mHf used during….?
Ex.] on board

16. 2. Vaporization and Boiling
Vapor pressure = the pressure exerted by a layer of the gas phase on the surface of a liquid or solid
High Vapor pressure = weaker IMF’s, weaker bonds, changes to gas phase easily
Low vapor pressure = STRONGER IMF’s, stronger bonds, and prefers to remain a liquid phase

17. Table H Vapor Pressure of Four Liquids

18. 3. Boiling Point vs. Normal Boiling Point
Boiling Point = temperature at which vapor pressure of the liquid equals the atmospheric pressure of the surroundings
NORMAL
boiling point = temperature when the vapor pressure equals standard pressure [1atm]

19. What changes the boiling point?
Changes in atmospheric pressure cause changes in the boiling point
Low pressure at higher altitudes cause the boiling point to be lower than normal [pressure is lower than normal…]
High pressure occurring below sea level cause boiling points to increase […?]

20. Vapor Pressure… REVIEW…
Vapor pressure changes INDIRECTLY with variations is atmospheric pressure
Explain……
Vapor pressure is a function of IMF’s within the liquid phase
Stronger IMF’s = ________ vapor pressure
Weaker IMF’s = _________ vapor pressure

21. 4. Sublimation and Deposition

22. III. Temperature Average KE of particles within an area
Measured in Celsius or Kelvin
K = oC
Potential energy = stored energy; no temperature changes
Changes in KE = changes in Temperature; reflects Energy in motion

23. V. Gases Pressure Units and definitions:
Torr, atm, mmHg, kPa, Pa, etc. [on board]
Standard Pressure = ……….
Use Dimensional Analysis to convert from one unit to another!

24. a. KMT KMT = Kinetic Molecular Theory
Theoretical Model explaining how/why particles behave as they do
Based on ideal gas equation: PV=nRT
Describes the behavior of an ‘ideal gas’

25. A. Postulates [parts]
1- Gas particles move in straight-line, continuous, random motion
2- Have NO attractive forces due to large distances between molecules
3- The volume of the particles themselves are negligible compared to the volume of the gas itself

26. Postulates cont’. 4- Particles have perfectly elastic collisions
5- Total Kinetic Energy of the system is proportional to the absolute temperature of the system

27. B. Ideal Gases vs. Real Gases
Have no attractive forces between particles
Particles have no relevant volume
Have attractive forces between their particles
Particles themselves have a definite volume

28. The MOST Ideal of the Real Gases are...
Most IDEAL Gases
Most IDEAL Conditions
Hydrogen
Helium
Why?...
Both have very small volumes
Both have very weak attractive forces
HIGH Temperature
Low Pressure
Why?...
Lots of Kinetic energy, moving very fast so little time for attractive forces
Large volume, lots of space, so little taken up by atoms themselves

29. c. Pressure Definition= amount of force per unit area
Units: Torr, atm, mmHg, kPa, Pa, etc.
Standard Pressure =
Use Dimensional Analysis to convert from one unit to another!

30. d. Gas Laws 1. Boyle’s Law
Boyle’s Law = changes in pressure cause changes in volume
Indirect relationship
Uses 2 sets of conditions for P and V, at a constant temperature

31. Boyle’s Law Equation and Calculations
P1V1 = P2V2
At constant Temperature!
A(n) ____________ Relationship between pressure and volume
Ex.] If the initial pressure inside a balloon is 0.95atm with a volume of 0.25L, what will the volume be when the pressure is decreased to 0.75atm and the temperature remains constant?

32. Boyle’s Law Examples cont.’
Ex.] The volume of gas inside a tank is 53.2L at a pressure of 0.55atm. What will the new pressure be when the volume is decreased to 35.7L at constant temperature?

33. 2. Charles’ Law Charles’ Law is a temperature and volume relationship
Changes in temperature cause changes in volume, at constant pressure
Temp line crosses volume axis at
–273 degrees celsius

34. Charles’ Law Equation and Calculations
Special Note:
ALL temperatures HAVE to be converted into KELVIN!!!
Temp oC = Temp K
Charles’ Law Equation V1 = V2 T1 T2 At constant Pressure! A(n) ______________ relationship!

35. Charles’ Law Examples cont.’
Ex.] The temperature of 0.33L of gas inside a balloon is 21oC. What will the volume be when the temperature changes to 1.0oC at constant pressure? Ex.] A 2.25L sample of air has a temperature of 25C. What will the temperature be when if volume changes to 1.13L at constant pressure?

36. 3. Gay-Lussac’s Law
This is a pressure and temperature relationship, at constant volume.
It is a ___________ relationship!
Temperatures need to be in KELVIN!!

37. Gay-Lussac’s Equation and Calculations
P1 = P2
T1 T2
Occurs at constant volume!!
Ex.] The pressure inside a container is 0.98atm at 100C. What is the new temperature when the pressure increases to 2.25atm?

38. 4. Combined Gas Law
Pressure, temperature, and volume condition changes can be related for two sets of conditions with the Combined Gas Law
P1V1 = P2V2
T T2

39. Combined Gas Law Example
Ex.] A 75mL sample of gas is at STP. What will the volume become if the temperature is raised to 75oC and the pressure is increased to 945 torr?

40. 5. Avogadro’s Law Established by the work of Avogadro
What value did he generate from his work with gases?
A moles vs. volume relationship at constant temperature and pressure
V1 = V2
n1 n2

41. 6. Ideal Gas Law
The “Ideal Gas Law” defines the variables of a gas during one set of conditions
Uses gas law constant, R, for calculations
R = L*atm/mol*K
PV = nRT
NOTES:
Pay attention to units
Use units of gas constant and convert accordingly
SINGLE SET OF CONDITIONS!!!

42. Ideal Gas Law Example
Ex.] Calculate the volume of 0.049mol of a gas whose pressure is 1.95atm at 3oC.
Ex.] Calculate the volume of 0.75mol of methane at 303K and a pressure of 0.758atm.

43. C. Van der Waals Equation
This is an alteration of the Ideal Gas Equation that accounts for the differences between ideal and real gases
Adds constants for specific substances to adjust volumes and attractive forces

44. F. Phase Diagrams
Phase Diagrams are temperature vs. pressure graphs for a substance
Diagrams allotropes and shows special temperatures:
Critical Point
Triple Point
Supercritical Fluids

45. Phase Diagram of Carbon

46. Phase Diagram for Carbon Dioxide

47. Phase Diagram of Water