Physical Science / Unit 2: Properties and States of Matter
2.4 Phase Changes
Notes
A phase change is a change of state. Energy is added or removed, but the substance stays the same.
- Melting (solid to liquid), freezing (liquid to solid), vaporization (liquid to gas, includes boiling and evaporation), condensation (gas to liquid), sublimation (solid to gas), deposition (gas to solid).
- Melting, vaporization and sublimation absorb energy. Freezing, condensation and deposition release energy.
- Water melts and freezes at 0 degrees C and boils at 100 degrees C.
- During a phase change the temperature stays constant; the added energy breaks the attractions between particles instead of raising the temperature.
Practice
What is the change from gas to liquid called?
Water vapor condensing on a cold glass is an example.
A pot of water boils at 100 degrees C while a stove keeps adding heat. What happens to the water's temperature while it boils?
The added energy goes into changing the phase, not the temperature.
Dry ice (solid carbon dioxide) turns directly into a gas at room temperature. This process is:
Solid to gas without becoming liquid is sublimation.
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