華南理工大：物理化學(xué)(雙語)02II

物理化學(xué)電子教案—第二章（下）2023/2/7Adiabaticprocess

InFig.PV:SlopeinAB：SlopeinAC：Inreversibleprocesstheworkdone（belowthelineAB）isbigthantheworkdone(belowthelineAC)inadiabaticreversibleprocess.T2023/2/7FcessInanisothermalexpansionheatcontinuouslyflowsintothesystem,andsothepressuredoesnotfallasmuchasinathermallyisolated,adiabaticexpansion.2023/2/7

Workinadiabaticprocess（1）cess.thereforebecause2023/2/7Abettercalculationmethod（2）anotherwaytocalculate

Thisequationistrueforalladiabaticexpansionsorcontractionsinvolvingaperfectgasornot,reversibleornot.2023/2/72.7realgasJoule-Thomsonexperiment

Joule在1843年所做的氣體自由膨脹實驗是不夠精確的，1852年Joule和Thomson

設(shè)計了新的實驗，稱為throttlingprocess。在這個實驗中，使人們對實際氣體的U和H的性質(zhì)有所了解，并且在獲得低溫和氣體液化工業(yè)中有重要應(yīng)用。2023/2/7throttlingprocessTheJoule-ThomsonexpansionconsistsofallowingagastoexpandthroughaporousplugfromaregionofhigherpressuretoaregionoflowerpressureasdepictedinFig.Theprocessiscarriedout

steadilyandadiabatically.2023/2/7throttlingprocessWhentheflowissufficientlyslow,thegashaswelldefinedpressureandtemperatureonbothsidesoftherestriction.2023/2/7UandHinthethrottlingprocessLeft,Surroundingscompressesgaseoussystem:work,systemgot：Adiabatic

Q=0，then：Right,gaseoussystemexpansion：work,surr.got:2023/2/7UandHinthethrottlingprocessthesumofwork:thenThrottlingprocessisconst.-enthalpyprocess!Itisisenthalpic.2023/2/7Joule-Thomsoncoefficient：

>0經(jīng)節(jié)流膨脹后，氣體溫度降低。

-TheisenthalpicJ-Tcoefficient是系統(tǒng)的強度性質(zhì)。因為節(jié)流過程的,所以當(dāng)：<0經(jīng)節(jié)流膨脹后，氣體溫度升高。

=0經(jīng)節(jié)流膨脹后，氣體溫度不變。2023/2/7Extentofreaction

20世紀(jì)初比利時的Dekonder引進反應(yīng)進度的定義為：單位：mol

isthestoichiometriccoefficientofcomponentB,negative-reactantsandpositive-products.2023/2/7extentofreaction

引入反應(yīng)進度的優(yōu)點：在反應(yīng)進行到任意時刻，可以用任一反應(yīng)物或生成物來表示反應(yīng)進行的程度，所得的值都是相同的，即：d=2023/2/7Ifthetransferofheatoccursatconstantvolume,andifnootherformsofworkarepermitted,(△U)v=Qv.Foraspecifiedchangeofstate△Uisindependentofhowthechangeisbroughtabout,thereforethesubscriptvcanbedroppedfromU:△U=Qv.Thesignificanceofthisequationisthatifwemeasuretheheattransferredatconstantvolumewecanidentifyitwiththechangeinathermodynamicstatefunction.Thereactionenthalpy2023/2/7Theanalogousresultforchanges

occurringatconstantpressure.△H=Qp.WhenthereisnoworkotherthanPV-work.Therelationbetween△Hand△U.TheenthalpyofasubstancediffersfromitsthermodynamicenergybyanamountpV.Itfollowsthat

△H=△U+[pV](products)-[pV](reactants)Forreactionsinvolvingonlysolidsandliquids:△H△U2023/2/7TherelationbetweenQpandQv

Whentheextentofreactionisunity:

or

2023/2/7Const.-pandconst.-Vheatofreactionreactantsproducts

（3）

（2)cons.V

and

products

Deducetherelationbetween2023/2/7Theheatatcons.volumeandcons.pressure反應(yīng)物生成物

（3）

（2）等容

生成物

Forpg，

P2V1-P1V1=P1V2-P1V1

2023/2/7Theequationofthermochemistry

U,H

arestatefunctions，所以方程式中應(yīng)該注明物態(tài)、溫度、壓力、組成等。對于固態(tài)還應(yīng)注明結(jié)晶狀態(tài)。例如：298.15K時

式中：

表示反應(yīng)物和生成物都處于標(biāo)準(zhǔn)態(tài)時，在298.15K，反應(yīng)進度為1mol

時的焓變。p代表氣體的壓力處于標(biāo)準(zhǔn)態(tài)。2023/2/7ThestandardmolarenthalpyofreactionEnthalpychangeAllproductsandreactantsbeingintheirstandardstatesattheTExtentofreactionis1molreactionReactiontemperature2023/2/7壓力的標(biāo)準(zhǔn)態(tài)隨著學(xué)科的發(fā)展，壓力的標(biāo)準(zhǔn)態(tài)有不同的規(guī)定：標(biāo)準(zhǔn)態(tài)用符號“”表示，

表示壓力標(biāo)準(zhǔn)態(tài)。最老的標(biāo)準(zhǔn)態(tài)為1atm1985年GB規(guī)定為101.325kPa1993年GB規(guī)定為1105Pa。標(biāo)準(zhǔn)態(tài)的變更對凝聚態(tài)影響不大，但對氣體的熱力學(xué)數(shù)據(jù)有影響，要使用相應(yīng)的熱力學(xué)數(shù)據(jù)表。2023/2/7壓力的標(biāo)準(zhǔn)態(tài)氣體的標(biāo)準(zhǔn)態(tài)：壓力為

的理想氣體，是假想態(tài)。固體、液體的標(biāo)準(zhǔn)態(tài)：壓力為

的純固體或純液體。標(biāo)準(zhǔn)態(tài)不規(guī)定溫度，每個溫度都有一個標(biāo)準(zhǔn)態(tài)。一般298.15K時的標(biāo)準(zhǔn)態(tài)數(shù)據(jù)有表可查。為方便起見，298.15K用符號表示。2023/2/72.9Hess’slawofconstantheatsummation1840年，根據(jù)大量的實驗事實赫斯提出了一個定律：反應(yīng)熱只與起始和終了狀態(tài)有關(guān)，與變化途徑無關(guān)。不管反應(yīng)是一步完成的，還是分幾步完成的，其熱相同，當(dāng)然要保持反應(yīng)條件（如溫度、壓力等）不變。Itstatesthatthestandardenthalpychangeinanyreactioncanbeexpressedasthesumofthestandardenthalpychanges,atthesametemperature,ofaseriesofreactionsintowhichtheoverallreactionmayformallybedivided.2023/2/7赫斯定律例如：求C(s)和

生成CO(g)的反應(yīng)熱。

已知：（1）

（2）

則（1）-（2）得（3）

（3）2023/2/7Enthalpyofformationofacompound沒有規(guī)定溫度，一般298.15K時的數(shù)據(jù)有表可查。生成焓僅是個相對值，相對于穩(wěn)定單質(zhì)的焓值等于零。standardmolarenthalpyof

formationTheenthalpychangesthatoccurwhenunitamountofthecompoundinitsstandardstateisformedfromitselementsintheirstandardstates： （物質(zhì)，相態(tài)，溫度）2023/2/7EnthalpiesofformationofcompoundsForexample：at298.15KThisisthestandardmolarenthalpyofformationofHCl(g)

：

Reactionenthalpy：

2023/2/7Definethereactionenthalpy

isthestoichiometriccoefficient,thenegativesigngoingwiththereactantandthepositivewiththeproduct.ThestandardenthalpyofreactionisthedifferenceH(products)-H(reactants),allsubstancesbeingintheirstandardstatesatthetemperatureT.2023/2/7EnthalpyofcombustionThesubscript“c”denotescombustion。Thesuperscript“”denotesallsubstancesbeingat

standardpressure.Thesubscript“m”denotesthebeing

1mol.Atstandardpressureand

reactiontemperature，thechangeof

enthalpyaccompanyingtotaloxidationofamaterialiscalled

Standardmolarenthalpyofcombustion.

Itisdenoted(substance,phase,temperature)2023/2/7燃燒焓指定產(chǎn)物通常規(guī)定為：金屬游離態(tài)顯然，規(guī)定的指定產(chǎn)物不同，焓變值也不同，查表時應(yīng)注意。298.15K時的燃燒焓值有表可查。2023/2/7燃燒焓例如：在298.15K及標(biāo)準(zhǔn)壓力下：則顯然，根據(jù)標(biāo)準(zhǔn)摩爾燃燒焓的定義，所指定產(chǎn)物如 等的標(biāo)準(zhǔn)摩爾燃燒焓，在任何溫度T時，其值均為零。2023/2/7Useoftheenthalpyofcombustion例如：在298.15K和標(biāo)準(zhǔn)壓力下，有反應(yīng)：（A）（B）（C）(D)則Thereactionenthalpyisgivenby：incalculatingtheenthalpyofareaction.2023/2/7Calculatetheenthalpyofformation該反應(yīng)的反應(yīng)焓變就是 的生成焓，則：例如：在298.15K和標(biāo)準(zhǔn)壓力下：usingenthalpiesofcombustion.2023/2/7

Kirchhoff`slaw1858年Kirchhoff提出了Thetemperature–dependenceofreactionenthalpies也是溫度的函數(shù)，只要將Cp-T的關(guān)系式代入，就可從一個溫度時的焓變求另一個溫度下的焓變。如有物質(zhì)發(fā)生相變，就要進行分段積分。2023/2/7

Adiabaticreaction求終態(tài)溫度的示意圖設(shè)反應(yīng)物起始溫度均為T1，產(chǎn)物溫度為T2，整個過程保持壓力不變：2023/2/72.12 絕熱反應(yīng)根據(jù)狀態(tài)函數(shù)的性質(zhì)可由 表值計算可求出從而可求出T2值2023/2/7PhasetransitionsDuringachangeofphaseofapuresubstance,suchasvaporization,melting,andsublimation,itstemperatureandpressureremainconstantwhileitsentropyandvolumeundergochanges.Thetemperature

andpressureofapuresubstanceconsistingoftwophasesinequilibriumarenotindependentvariables.2023/2/7ReversiblephasetransitionslgP*TH2O(l)H2O(g)T,P*enthalpyofphasetransitionvap

HmenthalpyvaporizationQp=vap

Hm=Qr2023/2/7Thetemperature–dependenceofenthalpy

H2O(l)H2O(g)H2O(l)H2O(g)T2,P*2T1,P*1vap

Hm,2=vap

Hm,1+Takeitasconst.PTheend2023/2/7JAMESPRESCOTTJOULEJAMESPRESCOTTJOULE(1818-1889)Englishphysicist,hadthestrengthofmindtoputscienceaheadofbeer.Heownedalargebrewerybutneglecteditsmanagementtodevotehimselftoscientificresearch.HisnameisassociatedwithJoule’slaw,whichstatesthattherateatwhichheatisdissipatedbyaresistorisgivenbyI2R.Hewasthefirsttocarryoutprecisemeasurementsofthemechanicalequivalentofheat;andthefirmlyestablishedthatworkcanbequantitativelyconvertedheat.2023/2/7JOSEPHLOUISGAY-LUSSACJOSEPHLOUISGAY-LUSSAC(1778-1850) Frenchchemist,wasapioneerinballoonascensions.In1804,Gay-Lussacmadeseveralballoonascensionstoaltitudesashighas7000m,wherehemadeobservationsonmagnetism,temperature,humidity,andthecompositionofair.Hecouldnotfindanyvariationofcompositionswithheight.In1809,hepointedoutthatgasescombineinsimpleproportionsbyvolume;andthisisstillcalledGay-Lussac’sworkonchlorinebroughtthescientistintocontroversywithSirHumphryDavy.2023/2/7JOSEPHLOUISGAY-LUSSACGay-Lussacassumedchlorinetobeanoxygen-containingcompound,whileDavycorrectlyconsidereditanelement,aviewthatGay-Lussaceventuallyaccepted.Heshowedthatprussicacidcontainedhydrogenbutnooxygen.Lavoisierhadinsistedthatoxygenwasthecriticalconstituentofacids,andGay-Lussac.Gay-Lussacwasoneofthetubing,allofwhichhadtobeimportedfromGerman,andtheFrenchhadanimportdutyonglasstubing.HeinstructedhisGermansuppliertosealbothendsofeachpieceoftubingandlabelthetubes“Germanair.”TheFrenchgovernmenthadnodutylistedfor“Germanair”,andhewasabletoimporthistubingdutyfree.2023/2/7WILLIAMTHOMSON,LordKelvinWILLIAMTHOMSON,LordKelvin(1824-1907) Irish-bornBritishphysicist,proposedhisabsolutescaleoftemperature,whichisindependentofthethermometricsubstancein1848.Inoneofhisearliestpapersdealingwithheatconductionoftheearth,Thomsonshowedthatabout100millionyearsago,thephysicalconditionoftheearthmusthavebeenquitedifferentfromthatoftoday.Hedidfundamentalworkintelegraphy,andnavigation.Forhisservicesintrans-Atlantictelegraphy,Thomsonwasraisedtothepeerage,withthetitleBaronKelvinofLarg.Therewasnoheirtothetitle,anditisnowextinct.2023/2/7HESSHESS(1802-1852)

俄國化學(xué)家，1802年出生于德國。在1836年提出了著名的赫斯定律。赫斯定律是熱化學(xué)的最基本規(guī)律。根據(jù)這個定律，熱化學(xué)公式可以互相加減，從一些反應(yīng)的反應(yīng)熱可求出另一些反