1. Section 3.3
Phase Changes

2. 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

3. Phase Change Diagram
Gas
Liquid
Solid

4. The temperature of a substance does not change during a phase change.
Energy is either absorbed or released during a phase change.
Endothermic change- is where the system absorbs energy from the surroundings.
Ex: Melting (also called fusion)- need heat
The amount of energy a substance must absorb to change from a solid to a liquid is called the heat of fusion.

5. Exothermic change- the system releases energy to its surroundings.
Ex: Freezing- release heat to freeze
Melting and Freezing
The arrangement of molecules in water become less orderly as water melts and more orderly as water freezes.
Substances do not have to be cold to freeze. Means becoming a solid.
Ex: Cookies baking

6. Vaporization and Condensation
Vaporization is an endothermic process.
Changing from a liquid to a gas.
Heat of vaporization is the amount of energy a substance must absorb to change from a liquid to a gas.
Evaporation
The process that changes a substance from a liquid to a gas temperature below the substance’s boiling point.

7. It takes place at the surface of a liquid.
Vapor pressure- the pressure caused by collisions of this vapor and the walls of the closed container.
Boiling- (for water) this is where the vapor pressure becomes equal to the atmospheric pressure.
Condensation-the phase change in which a substance changes from a gas to a liquid.
This is an exothermic process.
Water vapors transfer heat to an object and cools into a liquid. Ex: Dew on grass

8. Sublimation and Deposition
Sublimation- the phase change in which a substance changes from a solid to a gas or vapor.
This is an endothermic process.
Ex: Dry ice (solid carbon dioxide)
Deposition- the phase change in which a substance changes from a gas or vapor directly to a solid.
This is an exothermic process.
Ex: Frost