Phase changes involve a reversible physical change between solid, liquid, and gas states. Common phase changes include melting, freezing, vaporization, condensation, sublimation, and deposition. During a phase change, the temperature remains constant while energy is either absorbed or released. Melting and freezing involve a change between solid and liquid states, while vaporization and condensation change between liquid and gas states. Sublimation changes a solid directly to a gas, and deposition changes a gas directly to a solid.

1. Phase Changes A reversible physical change that occurs when a substance changes its state, solid, liquid or gas Melting, Freezing, vaporization, condensation, sublimation, and deposition are six common phase changes

2. Temperature and phase changes The temperature of a substance does not change during a phase change. Freezing and melting points are the same temperature Vaporization and Condensation points are the same

3. Energy and Phase Change Energy is either absorbed or released during a phase change Endothermic change absorbs energy (Melting) Exothermic change releases energy into surroundings (freezing) Heat of fusion is the amount of energy something absorbs in order to melt

4. Melting and Freezing The arrangement of molecules become more orderly as a substance freezes (becomes solid), and less orderly as something melts (becomes liquid).

5. Vaporization and Condensation Vaporization is an endothermic phase change of a liquid to a gas The amount of energy it takes to cause a substance to go from a solid to a liquid is called the heat of vaporization

6. Two types of Vaporization Evaporation- Takes place at the surface of a liquid (occurs below boiling). Vapor pressure is caused by the collision of particles with the walls of a container Boiling- when vapor pressure becomes equal to the atmospheric pressure substances boil

7. Condensation Condensation is when a substance turns from a gas to liquid. EX. include dew, water on the outside of a glass of lemonade on a hot day.

8. Sublimation and Deposition Sublimation is a phase change in which a solid goes directly to a gas (Dry Ice) Deposition is a phase change in which a gas becomes a solid (Frost)