3. What is a Phase Change?
• Is a change from one state of matter
(solid, liquid, gas) to another.
• Phase changes are physical changes because:
- It only affects physical appearance, not
chemical make-up.
- Reversible
4. What happens during a phase change?
• During a phase change,
heat energy is either
absorbed or released.
• Heat energy is released as
molecules slow down and
move closer together.
• Heat energy is absorbed
as molecules speed up
and expand.
6. Melting
• Phase change from a
solid to a liquid
• Molecules speed up,
move farther apart, and
absorb heat energy
7. Freezing
• Phase Change from a
liquid to a solid
• Molecule slow down,
move closer together
and release heat
energy.
8. Vaporization (Boiling)
• Phase change from a
liquid to gas. It occurs at
the boiling point of
matter.
• Molecules speed up,
move farther apart, and
absorb heat energy.
9. Evaporation
• Phase change from a
liquid to a gas on the
surface of a liquid
(occurs at all
temperatures).
• Molecules speed up,
move farther apart, and
absorb heat energy.
10. Condensation
• Phase change from a
gas to a liquid.
• Molecule slow down,
move closer together
and release heat
energy.
11. Sublimation
• Phase change from a
solid to a gas.
• Molecules speed up,
move farther apart, and
absorb heat energy.
17. 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.
• Freezing point: the temperature at which a
liquid turns into a solid when cooled.
20. Graphing a Phase Change
– 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?
