1. Phase Changes
Section 17.3 in YOUR book

2. Phase Change
A phase change is the reversible physical change that occurs when a substance changed from one state of matter to another.
Melting, freezing, vaporization, condensation, sublimation, and deposition are six common phase changes.

3. Temperature and Phase Change
One way to recognize a phase change is by measuring the temperature of substance as it is heated or cooled.
The temperature of a substance does NOT change during a phase change.

4. Energy and Phase Change
During a phase change, energy is transferred between a substance and its surroundings.
Energy is either absorbed or released during a phase change.
Transferred, surroundings
Energy, released
absorbs
Fusion
Releases

5. Energy and Phase Change
During an endothermic change, the system absorbs energy from its surroundings.
Amount of energy absorbed is the heat of fusion.
During an exothermic change, the system releases energy to its surroundings.
Transferred, surroundings
Energy, released
absorbs
Fusion
Releases

6. Energy and Phase Change
Ice absorbs energy as it melts.
Water releases energy as it freezes.
The amount of energy is the heat of fusion. The heat of fusion for water is 334 joules (J).
Melts
Freezes

7. Melting and Freezing
The arrangement of molecules in water becomes less orderly as water melts and more orderly as water freezes.
Melting
When ice is removed from the freezer heat flows from air to the ice.
As the ice gains energy, the molecules vibrate more quickly.
When all molecules have enough energy to move, melting is complete.
Arrangement, melts
Air
Gains
Move

8. Melting and Freezing Freezing
When water is placed in a freezer, energy flows from the water to the air in the freezer, and the water cools down.
As the energy of the molecules decrease, the molecules move more slowly.
When all of the molecules have been drawn into an orderly arrangement, freezing is complete.
Flows, cools
Decreases
Molecules

9. Vaporization and Condensation
The phase change is which a substance changes from a liquid into a gas is vaporization.
Vaporization is an endothermic process (substance absorbs energy).
Liquid
Endothermic
Surface
Gas
Vapor

10. Vaporization and Condensation
Evaporation takes place at the surface of a liquid and occurs at temperatures below the boiling point. Evaporation is the change from a liquid to a gas.
Vapor pressure is the pressure caused by collisions of this vapor and the walls of the closed container.
Liquid
Endothermic
Surface
Gas
Vapor

11. Vaporization and Condensation
Boiling
As you heat water, both the temperature and the vapor pressure of the water increase. When the vapor pressure becomes equal to the atmospheric pressure, the water boils.
Condensation
Condensations is the phase change in which a substance changes from a gas/vapor to a liquid.
This is an exothermic process.
Pressure
Equal
Liquid
Exothermic

12. Sublimation and Deposition
Sublimation is the phase change in which a substance changes from a solid to a gas/vapor.
Deposition is the phase change in which a gas/vapor changes directly into a solid without first changing to a liquid.
This is an exothermic process.
This is what causes frost to form on your car windows.
Solid
Directly
Exothermic

13. 3.3 Assessment
Answer questions 1-6. Write the question and the answer.
Complete the Writing in Science. Be sure to write with complete sentences.