1. 3.3 Physical Changes due to particle energy
Changes of State
3.3 Physical Changes due to particle energy

2. Melting A change from a solid to a liquid
Adding energy increases particle movement which helps particles overcome attraction to one another
When melting point is reached the solid will melt
Different substances have different melting points
Is the same temperature for a substance as its freezing point

3. Freezing Change of state from liquid to solid
Freezing point is same temp as substance’s melting point
Melting and freezing are reverse processes – melting adds energy and freezing removes it
Removing particle energy causes particles to get locked in place as particle movement slows and particle attraction takes hold.

4. Evaporation Change of substance from liquid to gas
Can occur at surface of liquid if substance is below its boiling point – liquid absorbs energy from surroundings
Sweat absorbs energy from body and as it evaporates, cools the body
Each substance has its own boiling point
Boiling is achieved when the pressure inside the bubbles equals air pressure.
Water boils at a lower temp at higher altitude because air pressure is lower.

5. Condensation Change of state from a gas to a liquid
Reverse of evaporation
Same temperature as boiling point at a given pressure
Particles clump together as they cool because particle energy is lost and attraction takes over
Energy is removed causing exothermic change

6. Sublimation and Latent heat
Change in state directly from a solid to a gas – ex: dry ice
Particles must gain enough energy to break their attraction
Endothermic reaction because energy is gained by the substance
Latent heat
Temperature is related to speed of particles
Temperature does not change during phase change; temp change takes place after phase change is complete