13 Thermal properties of materials Alevel考试物理课件.ppt

Thermalpropertiesofmaterials

Melting,boilingandevaporationSolution

Theenergysupplieddoesnotincreasethekineticenergy,butincreasesthepotentialenergyofthemolecules.Theincreaseinpotentialenergyisthelatentheatoffusionofthesolidandthelatentheatoffusion.

Whymeltingandboilingtakeplacewithoutachangeintemperature?Becauseitsactuallychangingthestateortheorganizationalstructureofthemoleculesoratomsiteffects.Itusestheenergynormallytochangethestatefromagastoaliquidorliquidtosolidorsolidtogas,etc.

Whyacoolingeffectaccompaniesevaporation?Inthecaseofevaporation,asitisasurfaceprocessandcantakeplaceatanytemperature,(whereheatisnotsuppliedfromoutsidegenerally),thelatentheatofevaporationistakenfromtheliquiditselfandinthecourseoftheprocess,theliquidlosesitstemperatureorcoolingtakesplaceintheliquid.Thatmeans,byevaporation,coolingcantakeplaceintheliquiditselfuntilsaturationhasbeenarrived,whennofurthercoolingcantakeplace.Actuallythisprincipleisusedingettingthewetbulbtemperature.

EgAssumingthattheatomsinironarearrangedinasimplecubiclattice,estimatethespacingbetweenatomsiniron.Thedensityofironis7900kgm-3anditsmolarmassis56×10-3kg.

SpecificheatcapacityTemperatureriseThermalenergysuppliedConstantmassThermalenergysuppliedConstanttemperaturerisemass

Wherecistheconstantofproportionalityknownasthespecificheatcapacityofthesubstance.(Jkg-1K-1)

EgCalculatethequantityofheatenergyrequiredtoraisethetemperatureofamassof810gofaluminumfrom20℃to75℃.Thespecificheatcapacityofaluminumis910Jkg-1K-1.

Thermal(heat)capacityThenumericalvalueofthethermalcapacityofabodyisthequantityofheatenergyrequiredtoraisethetemperatureofthewholebodybyonedegree.(JK-1)

EgAroomhasathermalcapacityof1.2MJK-1.Calculate