1. Announcements 1st HW answer key available Friday afternoon
LTEF poster due by 4:00 pm 10/1
2nd HW due on 10/8 or 10/9
Test on 10/11 or 10/12

2. Change of State
Vapor Pressure

3. What is Vaporization?
aka Evaporation
Change of state: liquid to gas

4. Is Evaporation Exo- or Endothermic?
Endothermic…why?
Must overcome the intermolecular forces
DH(vap) for H2O is 40.7 kJ/mol

5. Practical Uses for Vaporization
Most of the energy from the sun is used to evaporate water rather than warm the planet.
Evaporation cools the human body.
Discuss rates of evaporation and condensation on board.

6. What is the opposite of vaporization?
Condensation
Rate of evaporation vs. condensation

7. Vapor Pressure
Pressure of the vapor above a liquid when the rate of evaporation and condensation are equal.

8. Measuring Vapor Pressure

9. Measuring Vapor Pressure
Different liquids have different vapor pressures. Why?
How does temperature affect vapor pressure?

10. Temperature vs. Vapor Pressure
As T increases, vapor pressure increases
What happens when T gets 100ºC?
Boiling point: T at which the vapor pressure equals atm pressure.
For H2O:
T (ºC) P(torr)

11. Graphing Pvap vs. Temperature

12. Chemistry and Straight Lines

13. Chemistry and Straight Lines
Slope: - DHVAP / R
lnP = [-DH / R][1/T] + b
lnPT1 – lnPT2 = [DH / R][1/T2 – 1/T1]

14. Clausius Clapeyron Equation
ln[PT1 / PT2] = [DH / R][1/T2 – 1/T1]

15. Practice Problem
The vapor pressure of water at 25ºC is 23.8 torr and the heat of vaporization is 40.7 kJ/mol. Calculate the vapor pressure of water at 50ºC.

16. Heating Curve

17. Practice Problem 2
Calculate the enthalpy change associated with converting 1.00 mol of ice at –25.0 ºC to water vapor at 125 ºC and 1 atm pressure.
c(ice) = 2.09 J / g °C DH(fus) = 6.01 kJ/mol
c(liquid) = DH(vap) = 40.7 kJ/mol
c(steam) = 1.84

18. Phase Diagrams

22. What’s on the test? Multiple choice (~20 points) Ordering (~15 points)
Free response (~65 points)
Heating curve calculations
Phase diagram interpretations
Clausius Clapeyron manipulations
Unit cell calculations
Short answer questions