Unit 10- States of Matter

1
III. Changes of State

• Unit 10- States of Matter

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
Boltzmann Distribution
p. 477
5
A. Phase Changes

• Dynamic Equilibrium
• trapped molecules reach a balance between
  evaporation condensation

6
A. Phase Changes
p.478

• Vapor Pressure
• pressure of vapor above a liquid at equilibrium

v.p.

• depends on temp IMF
• directly related to volatility

temp
7
A. Phase Changes

• Boiling Point
• temp at which v.p. of liquid equals external
  pressure

• depends on Patm IMF
• Normal B.P. - b.p. at 1 atm

8
A. Phase Changes

• 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
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 1C
• 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 ?Hfuswhy?

• 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
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
(No Transcript)