1. Changes in State (PHASE CHANGES)—Notes
A Change in state (or phase change) is a change in the phase of matter due to a change of heat energy. Heat energy is either added or removed (gained or lost) from the matter.
A phase change is a physical change. This means that the substance is does not change chemically (no new substance is formed); it is still made of the same type of matter.
For example: If heat is added to ice (solid H2O) it will melt into water (liquid H2O), and eventually evaporate into water vapor (gaseous H2O).

2. Solid liquid gas
Losing energy (-)
Gaining energy (+)

3. When matter changes phase, heat is either gained (taken in) or lost (given away).
When a solid changes to liquid, heat is gained. This is known as melting.
When a liquid changes to solid,
heat is lost. This is known
as freezing.

4. When a liquid changes to gas, heat is added
When a liquid changes to gas, heat is added. This is known as vaporization.
When a gas changes to liquid, heat is lost. This is known as condensation.
When energy is absorbed, the molecules move faster.
When energy is released, the molecules move slower.

5. What’s the difference between boiling and evaporation?
Vaporization—the general term used to describe when matter changes from liquid to a gas.
This can occur in 2 different ways—evaporation or boiling
The temperature at which a liquid becomes a gas is a substance’s boiling point.

6. Evaporation
A liquid changes to a gas gradually, at temperatures below the boiling point.
For example, water may evaporate off of the surface of a pool, or pond, or glass of water at temperatures way below its boiling point of 100˚C. The water has to gain enough energy to escape the pressure of the air above it.

7. Boiling
A liquid changes to a gas when the substance reaches its boiling point.
For example, boiling will occur when a pot of water is placed over a hot stove coil. The bubbles form at the bottom of the pot and rise to the surface where the gas escapes.