1. Changes of State Lesson 14

2. Activator Why does ice cream melt?
Thermal energy allows flow of heat from a warmer substance to a cooler substance
Your ice cream absorbs thermal energy from the air and your hand
Added energy changes the ice cream from a solid to a liquid

3. Changes between a Solid and Liquid
How does the physical state of a substance relate to its thermal energy?
Substance
Liquid  more thermal energy
Solid  less thermal energy
Gas  most thermal energy
Change from a solid to a liquid  increase in thermal energy
Change from a liquid to solid  decrease in thermal energy

4. Melting Solid to liquid  melting
In most pure substances, melting occurs at a certain temperature  melting point
Melting point is a characteristic property

5. Melting How does an ice cube melt?
Energy to melt ice cube comes from air
Added thermal energy makes molecules vibrate  rises temp
At the melting point, the particles are vibrating so fast that they break free from their fixed positions
Ice cube melt

6. Imagine you are a particle of water in an ice cube
Imagine you are a particle of water in an ice cube. Suddenly someone plonks you into a beaker and puts it over a Bunsen burner flame!! What would you experience next??
You are here
Write a story, diary or design a cartoon strip to describe what is happening to you! Include as many of the words as you can from the box below!!
Solid, liquid, gas, particles, heat energy, kinetic (movement) energy, bonds, melting, boiling

7. Freezing Changing from liquid to solid
Freezing temperature  particles of a liquid are moving so slowly that they begin to form regular patterns
Cold makes the particles lose thermal energy which causes them to move more and more slowly

8. Changes between Liquid and Gas
Liquid to gas  vaporization
Vaporization occurs when liquid particles gain enough energy to form a gas
Two main types
Evaporation
Boiling

9. Liquid to Gas Evaporation: takes place only on the surface of a liquid
Ex. Shrinking puddle
Gains energy from the sun, air, ground
Added energy allows surface particles to escape into the air

10. Liquid to Gas Boiling: liquids change to gas below and on surface
Boiling causes bubbles
Boiling point: temp at which a liquid boils
Boiling point is used to help identify substances
Depends on pressure of air above it
Lower pressure  less energy required for liquid particles to escape

11. Condensation Opposite of vaporization
Condensation: particles in a gas lose thermal energy to form a liquid
Ex. Water vapor from a hot shower contacts the cool surface of the mirror and condenses into a liquid

12. Changes between Solid and Gas
Sublimation: surface particles of solid gain enough energy to form a gas
Particles do not pass through the liquid state
Ex. Dry ice
Solid carbon dioxide
Cannot exist as a liquid, so instead of melting, it turns directly into gas