1. Phase Changes

2. Review: 3 Phases (States) of Matter
Solid
Liquid
Gas

3. What is a Phase Change? A change from one state of matter
(solid, liquid, gas) to another.
Why are they physical changes?
It only affects physical appearance, not chemical make-up.
It is reversible.

4. Kinetic Energy
When temperature changes, molecules speed up/slow down resulting in a change in the average kinetic energy of molecules.

5. What happens during a phase change?
During a phase change, heat energy is either absorbed or released.
Heat energy is released as molecules move closer together.
Heat energy is absorbed as molecules move farther apart.

6. Potential Energy
During phase changes, temperature does not change. Molecules move closer together or farther apart, resulting in a change in the potential energy of the molecules.

7. Types of Phase Changes

8. Melting Phase change from a solid to a liquid
Molecules move farther apart, and absorb heat energy

9. Freezing Phase Change from a liquid to a solid
Molecule move closer together and release heat energy.

10. Evaporation
Phase change from a liquid to a gas on the surface of a liquid (occurs at all temperatures).
Phase change from a liquid to a gas from the inside and the surface (occurs at the boiling point).
Molecules move farther apart, and absorb heat energy.

11. Condensation Phase change from a gas to a liquid.
Molecule move closer together and release heat energy.

12. Sublimation Phase change from a solid to a gas.
Molecules move farther apart, and absorb heat energy.

13. Deposition Phase change from a gas to a solid.
Molecules move closer together and release heat energy.

14. Graphing a Phase Change

16. Melting & Boiling Points
Melting Point: The temperature at which a solid changes into a liquid.
Boiling Point: The temperature at which a liquid changes into a gas.
What is a Freezing point? Compare the freezing and melting points of water.

17. Summary
334 Joules
2260 Joules

18. Review Questions
Why is there no change in temperature during a phase change?
Define melting and boiling points.
What is the melting point and boiling point of water?
At what temperature does water freeze and become a solid?