《大学物理简明教程》 课件 17-1 PHASES OF MATTER

PhasesofMatter1Topicsinthislecture:Solid/Liquid/GasMelting/FreezingBoiling/CondensationSublimationLatentheatSpecificheatcapacity/MolarheatcapacityThermalexpansionBimetallicstripLinearexpansion/VolumeexpansionExpansionofholesConvertfromonephasetoanotherbyheatingorcoolingSOLIDLIQUIDGASPhasesofMatterConstantvolumeandshapeConstantvolumebuttakesshapeofcontainerFillsvolumeofcontainer2SOLIDLIQUIDGASPhaseDiagramPressureTemperaturemeltingboilingsublimationdepositioncondensationfreezingsolidliquid

liquidgas

solidgas

gasliquid

liquidsolid

T=triplepointsolid,liquid,gasinequilibrium3gassolid

PhaseDiagramsforothersubstancesWaterMostothersubstancesSolid-liquidlinehaspositiveslope.Solid-liquidlinehasnegativeslope.Pressureofskatesmeltsthewaterandletstheskaterslide4L=latentheat(J/kg)m=massofsample(kg)Q=heatenergy(J)SPECIFICLATENTHEAT(L)istheheatneededtochangethephaseof1kgLatentHeat–changingphaseQuestion1:Howmuchheatisneededtomelt250gofice?Latentheatoffusionofwater=333kJkg-1Fusion=meltingVaporisation=boilingQuestion2:Howmuchheatisneededtovaporise250gofwater?Latentheatofvaporisationofwater=2257kJkg-1Thetemperatureremainsconstantduringphasechange5NowPAUSEthevideoandtrytosolveQ1andQ2.6Question1:Howmuchheatisneededtomelt250gofice?Latentheatoffusionofwater=333kJkg-17Question2:Howmuchheatisneededtovaporise250gofwater?Latentheatofvaporisationofwater=2257kJkg-1Whydoesboilingneedmoreenergythanmelting?Becausethemoleculesneedtobeseparated.HeatCapacity–heatingwithinaphaseSPECIFICHEATCAPACITYistheheatneededtoraisethetemperatureof1kg

by1KQ=heatadded(J)c=specificheatcapacity(J/kg.K)m=massofsample(kg)

T=changeintemperature(K)

8MOLARHEATCAPACITY(c’)istheheatneededtoraisethetemperatureof1

moleby1KQuestion3:Calculatethemolarheatcapacityofcopper(molarmass63.5g)ifittakesa30Wheater21.4minutestoraisethetemperatureof1kgofcopperfrom100°Cto200°C.MolarHeatCapacity

n=numberofmoles1mole=6.02x1023molecules=Avogadro’snumberNowPAUSEthevideoandtrytosolveQ3Question3:Calculatethemolarheatcapacityofcopper(molarmass63.5g)ifittakesa30Wheater21.4minutestoraisethetemperatureof1kgofcopperfrom100°Cto200°C.SummarySpecificLatentheatistheheatneededtochangethephaseof1kgSpecificheatcapacityistheheatneededtoraisethetemperatureof1kgby1KThetemperatureremainsconstantduringphasechangeMolarheatcapacityistheheatneededtoraisethetemperatureof1moleby1KSOLIDLIQUIDGASwaterOthersubstances

ThermalExpansion12ThermalExpansionProblemSolutionDesirableLiLfatTiatTfFractionalchangeinlengthis

proportionaltochangeintemperature=coefficientoflinearexpansionUnitsK-1Experimentalfact:SolidsQuestion4TheDanyang–KunshanGrandbridgeinChinaisthelongestrailwaybridgeintheworldat164.8km.Iftherailsaremadeofsteel,byhowmuchdoesthelengthofthebridgeexpandwhenthetemperaturerisesfrom0

Cto30

C?NowPAUSEthevideoandtrytosolveQ4Question4TheDanyang–KunshanGrandbridgeinChinaisthelongestrailwaybridgeintheworldat164.8km.Iftherailsaremadeofsteel,byhowmuchdoesthelengthofthebridgeexpandwhenthetemperaturerisesfrom0

Cto30

C?Howdoengineerssolvetheexpansionproblem?BimetallicstripStripsoftwodifferentmetalsweldedorrivetedtogether.Expanddifferentamountswhenheated,soforcedtobend.Usedtocontrolthermaldevices.E.gthermostat.WhathappenstoHoles?COLDSquare=samesizeHole=smallerSquare=samesizeHole=biggerSquare=biggerHole=biggerSquare=biggerHole=smallerHOTABCDNowPAUSEthevideoandtrytosolveWhathappenstoHoles?COLDSquare=samesizeHole=smallerSquare=samesizeHole=biggerSquare=biggerHole=biggerSquare=biggerHole=smallerHOTABCDAlldimensionsexpandwhenheated=CoefficientofvolumeexpansionHowisrelatedto?VolumeExpansion(andLiquids)Question5Ifyoufilla1Lglasstothebrimwithwaterat20

C.Andthenheattheglass(andwater)to40

C.Howmuchwaterspillsout?NowPAUSEthevideoandtrytosolveQ5Question5Ifyoufilla1Lglasstothebrimwithwaterat20

C.Andthenheattheglass(andwater)to40

C.Howmuchwaterspillsout?WhichoneofthegraphsofVagainstTmostcloselyshowsthechangeinvolumeofwaterbetween-10°Cand+10°CAnomalousExpansionofwaterWaterhasminimumvolume(maximumdensity)at4

CIcefloatsonpond(fishdon’tfreeze)AABCDEGases

Ifpressureconstant

foridealgasQuestion6Comparethevolumechange(V2/V1)for1m3ofsolid,liquidandgasfortemperaturerisefrom0Cto100C.Gasesexpandalargeamount.Caremustbetakentoventorpressurecanbuildup.NowPAUSEthevideoandtrytosolveQ6Question6Comparethevolumechange(V2/V1)for1m3ofsolid,liquidandgasfortemperatureri