1. Unit 10- States of Matter
III. Changes of State

2. A. Phase Changes

3. A. Phase Changes Evaporation
molecules at the surface gain enough energy to overcome IMF
Volatility
measure of evaporation rate
depends on temp & IMF

4. A. Phase Changes temp volatility IMF volatility Boltzmann Distribution
# of Particles
volatility
IMF
volatility
Kinetic Energy

5. A. Phase Changes Dynamic Equilibrium
trapped molecules reach a balance between evaporation & condensation

6. A. Phase Changes temp v.p. IMF v.p. Vapor Pressure
pressure of vapor above a liquid at equilibrium
v.p.
depends on temp & IMF
directly related to volatility
temp
temp
v.p.
IMF
v.p.

7. A. Phase Changes Patm b.p. IMF b.p. Boiling Point
temp at which v.p. of liquid equals external pressure
depends on Patm & IMF
Normal B.P. - b.p. at 1 atm
Patm
b.p.
IMF
b.p.

8. A. Phase Changes IMF m.p. Melting Point equal to freezing point
Which has a higher m.p.?
polar or nonpolar?
covalent or ionic?
polar
ionic

9. A. Phase Changes Sublimation solid  gas
v.p. of solid equals external pressure
EX: dry ice, mothballs, solid air fresheners

10. B. Heating Curves – sketch this in your notes
Gas - KE 
Boiling - PE 
Liquid - KE 
Melting - PE 
Solid - KE 

11. B. Heating Curves Temperature Change change in KE (molecular motion)
depends on heat capacity
Heat Capacity
energy required to raise the temp of 1 gram of a substance by 1°C
“Volcano” clip -
water has a very high heat capacity

12. B. Heating Curves Phase Change change in PE (molecular arrangement)
temp remains constant
Heat of Fusion (Hfus)
energy required to melt 1 gram of a substance at its m.p.

13. B. Heating Curves Heat of Vaporization (Hvap)
energy required to boil 1 gram of a substance at its b.p.
usually larger than Hfus…why?
EX: sweating, steam burns, the drinking bird

14. C. Phase Diagrams
Show the phases of a substance at different temps and pressures.

15. C. Phase Diagrams
The diagram on the last slide shows the phase diagram for water
Each region represents a pure phase
Line between regions is where the two phases exist in equilibrium
Triple point is where all 3 curves meet, the conditions where all 3 phases exist in equilibrium!

16. Phase changes by Name
Critical Point
Pressure (kPa)
Temperature (oC)

17. What are the variables plotted on a phase diagram?
C. Phase Diagrams
With a phase diagram, the changes in mp and bp can be determined with changes in external pressure
What are the variables plotted on a phase diagram?

18. C. Johannesson