The document explains the different types of phase changes that can occur when matter gains or loses thermal energy. It defines evaporation as a liquid changing to a gas when high-energy molecules at the surface break free, boiling as evaporation occurring within a liquid, condensation as a gas changing to a liquid when molecules near a surface become attracted to it, melting and freezing as a solid changing between phases by absorbing or releasing energy, sublimation as a solid changing directly to a gas, and deposition as a gas changing directly to a solid. All of these phase changes involve the transfer of thermal energy as molecules gain or lose kinetic energy.

2. Change of PhaseChange of Phase
March 3, 2015March 3, 2015

3. ObjectivesObjectives
1.1. Explain changes in phase according toExplain changes in phase according to
heat and energyheat and energy
2.2. Define each of the phase changesDefine each of the phase changes

4. Heat TransferHeat Transfer
 When matter changes phase, a transfer ofWhen matter changes phase, a transfer of
thermal energy is involvedthermal energy is involved

5. EvaporationEvaporation
Liquid changes to gasLiquid changes to gas
 Molecules that gainMolecules that gain
kinetic energy at the surfacekinetic energy at the surface
get bumped freeget bumped free
 Becomes gas phase aboveBecomes gas phase above
the liquidthe liquid

6. EvaporationEvaporation
 Molecules that leave the liquid have theMolecules that leave the liquid have the
most energymost energy
 Energy of the liquid decreasesEnergy of the liquid decreases
 Temperature of the liquid goes downTemperature of the liquid goes down
 EX. PerspirationEX. Perspiration

8. Would evaporation be a cooling process ifWould evaporation be a cooling process if
there were no transfer of molecular energythere were no transfer of molecular energy
from water to the air above?from water to the air above?

9. BoilingBoiling
 Evaporation occurring within a liquid asEvaporation occurring within a liquid as
well as its surfacewell as its surface
 Bubbles of vapor formBubbles of vapor form
in the liquid and arein the liquid and are
buoyed to the surface,buoyed to the surface,
where they escapewhere they escape

10.  Boiling like evaporation is a coolingBoiling like evaporation is a cooling
processprocess
 Boiling water is in thermal equilibriumBoiling water is in thermal equilibrium
 It is being cooled byIt is being cooled by
boiling as fast as itboiling as fast as it
is being heated byis being heated by
energy from theenergy from the
heat sourceheat source

11. Since boiling is a cooling process, would itSince boiling is a cooling process, would it
be a good idea to cool your hot, stickybe a good idea to cool your hot, sticky
hands by dipping them into boiling water?hands by dipping them into boiling water?

12. CondensationCondensation
 Gas to a LiquidGas to a Liquid
 High energy molecules close to the surfaceHigh energy molecules close to the surface
become attracted to the liquidbecome attracted to the liquid
 Hit the surface with increased kinetic energyHit the surface with increased kinetic energy
 Raising the temperature of the surfaceRaising the temperature of the surface
 Gas has a lot of energy to give upGas has a lot of energy to give up

14. If the water level in a dish of water remainsIf the water level in a dish of water remains
unchanged from one day to the next, canunchanged from one day to the next, can
you conclude that no evaporation oryou conclude that no evaporation or
condensation is taking place?condensation is taking place?

15. Melting and FreezingMelting and Freezing
Melting - solid to a liquidMelting - solid to a liquid
 heat is absorbed the molecules vibrateheat is absorbed the molecules vibrate
more and more breaking the attractivemore and more breaking the attractive
forcesforces

16. Freezing - liquid to a solidFreezing - liquid to a solid
 energy is taken from the liquid, molecularenergy is taken from the liquid, molecular
motion slows downmotion slows down
 attractive forces betweenattractive forces between
them bind them togetherthem bind them together

17. SublimationSublimation
 Molecules jump directly from solid phaseMolecules jump directly from solid phase
to gaseous phaseto gaseous phase
 Snow and ice melting on a hot sunny daySnow and ice melting on a hot sunny day
 Dry ice in airDry ice in air

18. DepositionDeposition
 Molecules jump directly from gas phase toMolecules jump directly from gas phase to
solid phasesolid phase
 Snow formingSnow forming
high in thehigh in the
atmosphereatmosphere