Phase Changes

Phase Changes

Where is this used?

• Conditioning of buildings, such as 'ice-storage'• Cooling of heat and electrical engines• Cooling: food, beverages, coffee, wine, milk products, green houses• Medical applications: transportation of blood, operating tables, hot-cold therapies• Waste heat recovery• Solar power plants• Spacecraft thermal systems• Thermal comfort in vehicles• Thermal protection of electronic devices• Thermal protection of food: transport, hotel trade, ice-cream, etc.• Textiles used in clothing• Computer cooling

Review: 3 Phases of Matter

• Solid

• Liquid

• Gas

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.

Types of Phase Changes

• Types of Phase Changes

Melting

• Phase change from a solid to a liquid

• Molecules speed up, move farther apart, and absorb heat energy

Freezing

• Phase Change from a liquid to a solid

• Molecule slow down, move closer together and release heat energy.

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.

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.

Condensation

• Phase change from a gas to a liquid.

• Molecule slow down, move closer together and release heat energy.

Sublimation

• Phase change from a solid to a gas.

• Molecules speed up, move farther apart, and absorb heat energy.

Deposition

• Phase change from a gas to a solid.

• Molecules slow down, move closer together and release heat energy.

Graphing a Phase Change

What is wrong with this picture?

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.

Summary

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?