1. Phase Changes, Heat of Fusion, and Heat of Vaporization
States of Matter
Phase Changes, Heat of Fusion,
and Heat of Vaporization

2. Phases of Matter: (review)
Solid
matter that has definite volume and definite shape
Liquid
matter that has definite volume but indefinite shape
Gas
matter that has indefinite volume and indefinite shape 

3. Phase Change Descriptions:
Melting
the change from solid to liquid.
Freezing
the change from liquid to solid.
Evaporation (vaporization)
the change from liquid to gas .
Condensation
the change from gas to liquid .
Sublimation
the change from solid to gas .
Deposition
the change from gas to solid .

4. Changes of State

5. Phase Change Diagram (Heating/Cooling Curve)
condensing
Boiling Point
evaporating
Melting
Point
freezing
melting

6. Heat of vaporization: (Hvap) the energy absorbed to change one
•Heat of fusion: (Hfus)
the energy absorbed to change one mole of a substance from a solid to a liquid. (melting)
Heat of vaporization: (Hvap)
the energy absorbed to change one
mole of a substance from liquid to
gas. (vaporizing)

7. NO TEMPERATURE CHANGE OCCURS DURING A PHASE CHANGE!

8. Hvap
condensing
evaporating
Hfus
freezing
melting

9. When moving UP the curve, the Hfus and Hvap will be POSITIVE (+) because they are endothermic processes
When moving DOWN the curve, the Hfus and Hvap will be NEGATIVE (-) because they are exothermic processes

10. Hvap Exothermic H = (-) Hfus Endothermic H = (+) condensing
evaporating
Hfus
Endothermic
H = (+)
freezing
melting

11. Calculations with Phase Changes
Example 1: How much energy would it take to completely melt a 7.20 mol sample of ice at 0°C? The heat of fusion (Hfus) of H2O is 6.02 kJ/mol.

12. Calculations with Phase Changes
Example 2: How much energy would it take to completely melt a 15.0 g sample of ice at 0°C? The heat of fusion (Hfus) of H2O is 6.02 kJ/mol.
What must we do first?

13. Calculations with Phase Changes
Example 3: How much energy would be released when .456 g of water vapor (gas) at 100°C condense completely? The heat of vaporization (Hvap) of H2O is 40.7 kJ/mol.