Physical ChangePhases of Matter

Waters Phases:

“Ice” “Water”

“Vapor” They might seem completely different…

But are they really?

***You learned about the details of phases themselves in earlier grades. We are going to focus on WHY and HOW they change.

Kinetic Theory of Matter:

SolidLiquid

Gas

The kinetic theory of matter states that all matter is made of small particles that are in random motion and that have space between them. This means that no matter what phase matter is in, it is made of separate, moving particles.

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.

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…

Energy of the Phases:

Q: What is the ONLY real difference between each phase?

A: The amount of energy the molecules have!

Solids

• Very little energy– 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 atomsin a solid are doing (if we could see them)

Liquids

• “Medium” Energy– 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 atomsin a liquid are doing (if we could see them)

Gases

• “High” amount of Energy– 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 atomsin a gas are doing (if we could see them)

Energy of the Phases Review:

• Solid:Q: Would you describe this as having

a

high, medium or low amount of energy?

• Liquid:Q: Would you describe this as having

a

high, medium or low amount of energy?

• Gas:Q: Would you describe this as having

a

high, medium or low amount of energy?

Q: What is the ONLY real difference between each phase?

A: The amount of energy the molecules have!

Changing from Phase to Phase

Description of Phase Change

Term for Phase Change

Heat Movement During Phase Change

Temperature Change During Phase Change

Solid to liquid Melting Heat goes into the solid as it melts.

None

Liquid to solid Freezing Heat leaves the liquid as it freezes.

None

Liquid to gas Vaporization, which includes boiling and evaporation

Heat goes into the liquid as it vaporizes.

None

Gas to liquid Condensation Heat leaves the gas as it condenses.

None

Solid to gas Sublimation Heat goes into the solid as it sublimates.

None

Heat and Temperature Changes

Changing from Phase to Phase Review:

Solid

Liquid

Gas

Water is a great example because we are all so familiar with it!

Melting

Vaporizing

Freezing

Condensing

Q: What do we have to do to make a phase change to a new phase?

A: Increase or decrease the energy of the molecules in the substance!

Q: As a substance experiences a phase change, what are the processes called?

A: Melting, Freezing, Vaporizing (Boil and Evap.), Condensing

Q: When we change the phase, have we made a new substance?

A: NO! IT IS STILL WATER (H2O)!

***No change in the substance = Physical Change!

Heat and Temperature ChangesQ: If a sample of water was measured to be at 65 degrees Celsius,

what phase would it be? A: LiquidQ: If a sample of water was measured to be at 112 degrees Celsius,

what phase would it be? A: GasQ: A pot of water is boiling on a stove. How do you know for sure that

the pot and the water sample have different evaporation points?A: Water is already changing phase (boiling); the pot hasn’t even

melted yetQ: You open your freezer door and a small amount of your ice cubes

instantly turn to water vapor. What kind of change is this?A: Physical Change (solid water can also change phase when the

air pressure changes suddenly; like when you open a freezer door)

More Review: