1. Changes of State

2. Energy and Changes of State
Change of State:
Change of a substance to one physical form to another
Physical changes
Identity of the substance does not change
Ex: ice, liquid water, and steam are all the same substance.
State of matter is based on the amount of energy in the substance
to change the state of matter you add or take away energy.
Ice – little energy
Liquid water – moderate energy
Steam – a lot of energy

3. Melting: Solid to Liquid
Change of state from a solid to liquid
Melting ice
Adding energy increases temperature and causes the particles to move faster.
Melting Point:
Temp. at which a substance changes from a solid to a liquid
Different substances have different melting points
Energy added to a solid is used to overcome the attraction between particles
Endothermic Change:
Energy is gained by the substance as it changes state

4. Freezing: Liquid to Solid
Change of state from a liquid to a solid.
Freezing Point:
Temp. at which liquids turn to solids
Attraction must overcome the motion of the particles
Removal of energy will cause the particles to lock in place
Exothermic Change:
Removal of energy

5. Evaporation: Liquid to Gas
Change of a substance from a liquid to a gas
Occurs at the surface of a liquid below the boiling point
Boiling:
Change of a liquid to a gas throughout the liquid
Occurs when the pressure inside the bubbles equals the outside pressure
Boiling point changes with atmospheric pressure
Lower the pressure lower the boiling point

6. Condensation: Gas to Liquid
Change of state from gas to liquid
Condensation Point:
Temp. at which a gas becomes a liquid
Exothermic change
Energy is removed and particles clump together when the attraction between them overcomes the motion

7. Sublimation: Solid to Gas
A solid changes directly to a gas
Endothermic change
Energy is added and the particles move quickly breaking the attraction between them

8. Change of Temp. vs. Change of State
Temp. is related to the movement of the particles
Temp. of a substance does not change until the change of state is complete

9. Changing States of Matter
Overview
+ heat
+ heat
Solid
Gas
Liquid
melt
evaporate
freeze
condense
- heat
- heat