1. Phase Changes

2. Phases
When 2 states are present at the same time, we describe each as a phase.
Here, we see 2 phases of water:
Solid Phase
Liquid Phase

3. Phase Change Definition
A Phase Change is the reversible physical change that occurs when a substance changes from one state of matter to another.
There are 6 common phase changes
Melting
Freezing
Vaporization
Condensation
Sublimation
Deposition

4. Deposition
Condensation
Vaporization
Sublimation
Melting
Freezing

5. Phase Change
NOTE:
The temperature of the substance DOES NOT change during a phase change!!!!
All phase changes are related to energy and temperature.

6. Energy during Phase Changes
Law of Conservation of Energy
Neither created or destroyed.
Transferred or Transformed
In phase changes, energy is either absorbed or released.
Endothermic – energy is absorbed.
Ice melting
Exothermic – energy is released.
Water freezing

9. Phase Diagrams

10. Phase Diagrams

12. Triple and Critical Point
The Triple Point is where the substance exists in all 3 states.
The Critical Point is where, under extreme high temps and pressure, the liquid and gaseous states are indistinguishable.

13. Melting & Freezing
Water is a molecule made up of 2 atoms of Hydrogen and 1 atom of Oxygen.
The arrangement of molecules becomes less orderly as water melts.
The arrangement of molecules becomes more orderly as water freezes.

14. Melting Endothermic process
Heat energy is transformed into increased kinetic energy.
Causes molecules to vibrate more rapidly.
Some gain enough to overcome the attractive forces and move from the fixed locations.
This is the melting point.
Any energy gained after the phase change increases the average kinetic energy and the temperature rises.

15. Freezing
Exothermic
Average kinetic energy (Ke) decreases causing molecules to slow down.
At the freezing point, the attractive forces begin to draw the molecules into an orderly arrangement.
Continues until all have been fixed.
Any energy removed after the phase change is complete decreased the average kinetic energy of the molecules and the temperature decreases.

16. Vaporization
Vaporization happens when a substance changes from a liquid into a gas.
Endothermic
Heat of vaporization
Water gains 2258 J of energy when it vaporizes at 100° C.
2 vaporization processes
Boiling
Evaporation
Takes place at the surface of a liquid
Occurs at temps below the boiling point

17. Evaporation
Process that changes a substance from a liquid to a gas at temps below the boiling point.
In a closed container:
Water vapor collects above the liquid
Pressure caused by molecules colliding with container is called vapor pressure.
Pressure increases as temp increases.

18. Boiling
As you apply heat energy, temperature and vapor pressure increase.
When vapor pressure = atmospheric pressure, the water boils.
Called the boiling point.
Depends on Atmospheric Pressure
Higher elevations have less atmospheric pressure
Takes longer to cook food.

19. Condensation
The phase change in which a substance changes from a gas to a liquid.
The water vapor transferred heat to the glass and condensed into a liquid.

20. Sublimation & Deposition
Sublimation is the phase change from a solid to a gas without going through the liquid phase.
Endothermic
Dry Ice
Deposition is the phase change from a gas to a solid without going through the liquid phase.
Exothermic
Frost on windows