1. Physical Change Phases of Matter

2. Waters Phases: “Ice” “Water” “Vapor”
They might seem completely different…
But are they really?
***You learned about the details of phases
themselves in 7th grade. We are going to
focus on WHY and HOW they change.

3. Phases & States of Matter
Today’s two big points:
All phases are dependant upon the amount of thermal (heat) energy the substance
And how the energy affects the bonds between molecules in the substance.

4. Property you need to know:
If a substance is a solid, liquid, or gas at a certain temperature: That is a Property of that substance!
EX: Water is a good example since it is so simple!
<0 degrees Celsius = Solid
(if you stuck a thermometer in a solid piece of “ice” what would be a temperature you would expect?)
>0 degrees Celsius = Liquid
(if you stuck a thermometer in a glass of liquid water what would be a temperature you would expect?)
>100 degrees Celsius = Gas
Water is pretty much the ONLY substance that changes phase at these temperatures. For example: Nitrogen will still be a gas at -196 degrees Celsius!!! Nitrogen will MELT at -210 degrees Celsius (-346 F)!!!
***All substances change phase at a certain temperature unique for that substance. “Hot” and “cold” don’t matter…

5. Energy of the Phases:
Q: What is the ONLY real difference between each phase?
A: The amount of energy the molecules have!

6. Solids Very little energy Strong Bonds Molecules very close together
Not enough energy to break the bonds between molecules
Strong Bonds
Definite Shape (doesn’t change)
Definite Volume (can measure it)
Molecules very close together
This picture shows what the atoms
in a solid are doing (if we could see them)

7. Liquids “Medium” Energy “Medium” Bond Strength
Some bonds get broken – but they keep reforming.
“Medium” Bond Strength
No Definite Shape (Takes shape of “container”)
Definite Volume (Can measure it)
Not as tightly packed together
Can move around some (“flow”)
This picture shows what the atoms
in a liquid are doing (if we could see them)

8. Gases “High” amount of Energy “Weak” Bond Strength Very spread out
Enough energy to break the bonds
“Weak” Bond Strength
No Definite Shape (can’t see it)
No Definite Volume (difficult to measure)
Very spread out
Moving freely through container
This picture shows what the atoms
in a gas are doing (if we could see them)

9. Energy of the Phases Review:
Solid:
Q: Would you describe this as having a
high, medium or low amount of energy?
Liquid:
Gas:
Q: What is the ONLY real difference between each phase?
A: The amount of energy the molecules have!

10. Changing from Phase to Phase Review:
Water is a great example because
we are all so familiar with it!
Melting
Solid
Freezing
Vaporizing
Liquid
Condensing
Q: When we change the phase, have we made a new substance?
Q: As a substance experiences a phase change, what are the processes called?
Q: What do we have to do to make a phase change to a new phase?
Gas
A: NO! IT IS STILL WATER (H2O)!
A: Melting, Freezing, Vaporizing (Boil and Evap.), Condensing
A: Increase or decrease the energy of the molecules in the substance!
***No change in the substance = Physical Change!