资源描述：
《工程热力学 06(哈工大)new》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、CHAPTER6ENTROPYANDTHESECONDLAW6.1IntroductionWehavenowdevelopedtheFirstLawofThermodynamicsforbothclosedandopensystems,andshownhowitmaybeusedtosolvepracticalproblems.ButtheFirstLawisnottheendofthestory.TherearemanyimaginableprocesseswhichsatisfytheFirstLaw,but
2、areneverthelessdon'tseemtohappen.Weneedanotherprinciple,orlaw,"toexplainwhynot.Inthischapter,weintro-ducethisprinciple{thesecondlawofthermodynamicsandthenewpropertyassociatedwithit,theentropy.6.2PossibleandImpossibleProcessesOfallprocesseswhichsatisfytheFirs
3、tLaw,someactuallyhappenandsomeneverdo.Ifafewicecubesareaddedtoathermosbottlecontainingboilingwater,theicespontaneouslymeltsandtheinitially-hotwatercools.Whenequilibriumisreached,onlywarmwaterisleft.Thereverse,however,neverhappens:warmwaterhasneverbeenobserved
4、tospontaneouslytransformintohotwater+icecubes,eventhoughitispossibletodosoinawaywhichconservesenergy.Ifarubberballisheldaboveatableandthendropped,itbouncesafewtimesandcomestorest.Theinitialgravitationalpotentialenergyoftheballisconvertedtointernalenergyoftheb
5、all(andpossiblyofthetable):theballendsupslightlywarmerthanitbegan.Thereverseprocess
6、aballcoolingo slightlyandjumpingo atable{hasneverbeenobserved,althoughitcouldconserveenergy.Infact,foreveryprocessthatreallyhappens,thetime-reversedversion
7、inwhichtheinitialan
8、d nalstatesofthesystem+environmentareswitched
9、neverseemsto.Eggsbreakwhendroppedonthefloor;brokeneggshaveneverbeenseentounbreak"andriseo thefloor.Heatflowsspontaneouslyfromahightemperaturebodytoalowtemperatureoneitcontacts;ithasneverbeenobservedtoflowspontaneousl
10、yfromlowtemperaturetohigh.Aheliumballoonslowlydeflatesduetodi usionofheliumatomsthroughtheballoon127CHAPTER6.ENTROPYANDTHESECONDLAW128skin;adeflatedballoonhasneverbeenobservedtospontaneouslyinflateduetoheliumatomsdi usingfromthesurroundingstotheinterior.Despitet
11、heobservedone-waynatureofrealprocesses,theFirstLawmakesnodistinctionbetweenpossibleprocessandtheirimpossibletime-reversedver-sions.Consider,forexample,aclosedsystemwhichundergoesaprocessd
