1. Phase Changes Physical Science
Chapter 3 Section 3

2. Science Journal Entry #56
Describe the differences in the kinetic energy (movement) of particles in solids, liquids, and gases.

3. Science Journal Entry #57
Differentiate between Plasma And the Bose-Einstein Condensate.

4. Science Journal Entry #58
Explain how the vaporization by evaporation (of water) is different than vaporization by boiling water.

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

6. Energy and Phase changes
During a phase change, energy is transferred between a substance and its surroundings. The directions of the transfer depends on the type
of phase change.
Thermal Energy (Heat) is either absorbed or released during a phase change.
An endothermic process means that the object is absorbing energy from its surroundings.
During an exothermic process, thermal energy
is released into the environment from the object.

7. Temperature and Phase Change
One way to recognize a phase change is by measuring the temperature of a substance as it is heated or cooled.
The temperature of a substance does not change during a phase change. Consider the phase change of Naphthalene, a compound that is sometimes used in mothballs.

8. Freezing Phase of Naphthalene
If liquid naphthalene is placed in an ice-water bath, the temperature of the liquid will drop until it reaches 80o Celsius. But at 80o Celsius, the temperature of the naphthalene stops decreasing. The temperature remains at 80o Celsius, until freezing is complete. Therefore the freezing point of naphthalene is 80o C.

9. Freezing Point is the Melting Point
If heat is then added to naphthalene, it will melt until it reaches 80o C and it will stay at that temperature until melting is complete. This would be the melting point of naphthalene.
After melting is complete, the temperature will begin to rise again until it reaches 218o C. It will stay at that point until boiling is complete. This would be considered the boiling point of naphthalene.

10. Heating curve for naphthalene

11. Melting
Melting:
In ice, attractions between water molecules keep the molecules in fixed positions.
At the melting point of 0 degrees Celsius, some molecules gain enough energy to overcome the attractions and move from their positions.
Another name for melting is fusion. The heat of fusion is the amount of energy required to melt a substance.

12. Freezing
Freezing:
When liquid water is placed in a freezer, energy flows from the water to the air of the freezer and the water cools down.
As the average kinetic energy of its molecules decreases, they move more slowly.
The arrangement of molecules in water becomes less orderly when water melts and more orderly as water freezes.

13. Vaporization
The phase change in which a substance changes from a liquid into a gas is vaporization. Vaporization is an endothermic process. The amount of energy needed for a substance to vaporize is called the heat of vaporization.
The two vaporization processes are boiling and evaporation.

14. Evaporation
Vaporization and evaporation are not the same process. Evaporation takes place at the surface of liquid and occurs at temperatures below the boiling point.
An example of evaporation is a puddle outside that dries out when the sun comes out.
Evaporation occurs because some molecules near the surface are moving fast enough to escape the liquid and become water vapor. A vapor is the gaseous phase of a substance that is normally a solid or liquid at room temperature.

15. Evaporation in a Closed Container
As the water evaporates in a closed container, the water vapor collects above the liquid.
Collisions of this vapor and the walls of the container occur producing vapor pressure.
Vapor pressure is increased when temperature increases.

16. Boiling
When you boil water on the stove, the temperature and the vapor pressure of the water increases.
When the vapor pressure becomes equal to atmospheric pressure, the water boils. The temperature at that point is called the boiling point.
The normal boiling point of water is 100o Celsius at sea level.

17. Boiling Point
Atmospheric pressure is not the same everywhere. For instance in Denver, Colorado atmospheric pressure is less and water can boil as low as 95 degrees Celsius.
Boiling occurs when some water molecules below the surface of the liquid have enough kinetic energy to overcome the attraction of neighboring molecules.

18. Condensation
Condensation is the phase change in which a substance changes from a gas or vapor to a liquid. Condensation is an exothermic process.
You have seen condensation when water vapor condenses into water on a glass of ice tea in the summer.
This also occurs on the bathroom mirror after your shower.

19. Sublimation and Deposition
Sublimation is the phase change in which a substance changes from a solid to a gas or vapor without first becoming a liquid.
Dry ice (solid carbon dioxide) sublimes. It goes from a solid to a gas without ever becoming a liquid so it is used in shipping things that much stay cold without getting wet.
Deposition occurs when a gas or vapor changes to a solid without first becoming a liquid. Frost on your window is the winter is an example of this.

20. Particle Movement and Location

21. Phase Changes

22. Processes in Phase Changes