The second Law課堂版

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1、TheSecondLaw ofThermodynamicsChapter1dealtwiththefirstlawofthermodynamics,theconservationofenergyandenergytransferintermsofheatandwork.Thischapterdealswithanotherthermodynamicproperties,entropy,whichisalsoastatefunction.Thefirstlawofthermodynamicsaccountsfortheenergiesinvol

2、vedinsuchaconversionbutplacesnolimitsontheamountsthatcanbeconverted.Thesecondlawisconcernedwithlimitsontheconversionof“heat”into“work”byheatengines.StatementforthesecondlawTherearequiteafewequivalentwaystostatethesecondlaw.Ifthestatementsarecorrect,theyareallequivalent.Some

3、arehardertounderstandthanothers;someareincludedonlyforhistoricalpurposes.Ithinkthefollowingwayofstatingthesecondlawisuseful.1)Everythermodynamicsystempossessesanextensivestatefunctioncalled“theentropy”whichcanbecalculatedbyareversible(thatis,aquasi-staticlimitofarealprocess

4、)pathfromanarbitrarilychosen“ReferenceState”byintegratingtheheatabsorbedbythesystemdividedbytheabsolutetemperatureofthesystem.Inotherwords,“Entropy,thestatefunction,existsforeverysystem...”2)Duringanyobservableprocess,theentropyofasystemplusitssurroundings(togetherdefininga

5、nisolatedsystemoruniverse)neverdecreases.And,inotherwords,“...anditalwaysincreasesfortheuniverse”)StatementforthesecondlawClausiusHeatisnotobservedtopassspontaneouslyfromabodyatlowtemperaturetoabodyathighertemperature.Kelvin:Itisimpossibletocontinuouslyperformworkbycoolinga

6、bodytoatemperaturebelowthatofthelowesttemperatureofitssurroundings.Ostwald:Aperpetualmotionmachine“ofthesecondkind”hasneverbeenobserved.(Aperpetualmotionmachineofthesecondkind“runsforever.”)Caretheodory:Thisisthemostelegant(andhardesttounderstandandapply,perhaps)asitrequire

7、sthefewestunderlyingassumptions.StatementforthesecondlawIntheneighborhoodofeverythermodynamicstatethatcanbereachedbyareversiblepath,thereexistsstatesthatcannotbereachedalongareversibleadiabatic(isentropic)path;or,inotherwords,whichcanbereachedeitherirreversiblyornotatall.Fi

8、nally,thesecondlaw(itisreallyanaxiom—ithasneverbeenproved;onlyneverdisproved.)LESS

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