Physical Change Phases 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 7th grade. We are going to focus on WHY and HOW they change.

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 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)

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)

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)

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!

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!