应用地球化学：10年地化课件（复习）

AppliedGeochemistryPartOne

GeochemicalTheory1.Somebasicconcepts

1.1Atoms

Atomsarethebasicparticlesengagedinchemicalreactions.Theinnerstructuresoftheatomsarethemaindeterminantsofthechemicalandphysicalcharacteristicsofmaterials.Asatinnyparticle,theradiusofanatomisonlyabout10-10m.Theradiusofthenuclearofanatomisevenfarsmaller,10-14~10-15m.Thatmeansanatomisnearlyempty.

Atomsconsistofanucleus（核）ofprotons（N）andneutrons（Z）surroundedbyelectrons.Astheatomicnumberincreases,thenumberofnucleuscharges(1unitnucleuscharge=1.60*10-19C)increasesaswell.Theprotons,neutronsandelectronsofanatommakeupanelectromagneticsystem.Anucleusispositivelycharged,butthesurroundedelectronsarenegativelycharged.Thatiswhythewholeatomiselectricallyneutral.Nuclearstabilityarerelatedto(1)theparityofthenumberofprotons(Z)andthatofneutrons(seealsoChapter2).(2)theratioofthenumberofneutronstothatofprotons.N/Z.N/Zofnucleusofelementwithitsatomicnumbersmallthan20isroughlyequalto1.Itmeansthatsuchanuclearismoststablebecauseinthiscasethebindingenergyinsidethenuclearisinitsultimateextent.

ElectronicStructureofAtomsElectronsofatomcircumvolvearounditsnucleusinhighspeeds.Becausetheelectrons’movementhasnofixedorbits,electronicclouds（电子云）areformedintheouterofthenucleus.Theheavyareaofelectronicclouds—anareawhereelectronsappearmostfrequently—iscalledelectronicshell.1.2THEELEMENTS

Geochemistry(地球化学):Geochemistrydealswiththeabundance（丰度）anddistribution（分配）oftheelements。

Abundance（丰度）：Thecontentofanelementinanygeologicalmass(orbody).Distribution（分配）：Thelocalcontentofanelementinageologicalbody(mass).

Theabundanceanddistributionoftheelementsdependontheirphysicalandchemicalproperties.Intrue,thesepropertiesdependontheelectronicstructureoftheatomsandvarysystematicallywiththenuclearcharge(atomicnumber).(1)Abundanceoftheelements

Onegoalofgeochemistryisthedeterminationoftheabundanceoftheelementsinnature.Thisinformationisneededtodevelophypotheses（假说）fortheoriginoftheelementsandofthestructureoftheuniverse.Thesehypothesesareonlyasgoodasthechemicaldataandassumptionsonwhichtheyarebased.Thesedataareobtainedinmanydifferentways,andthequalityandquantityoftheresultsvaryfordifferentmaterialsandfromelementtoelement.A.AbundanceoftheelementsintheUniverseTheuniverseismadeupmainlyofstars,nebulae(星云),andinterstellargas(星际气体)anddust.Ourknowledgeoftheabundanceoftheelementsintheuniversecomesfromtwomajorsources:A.Spectroscopicanalyses（光普分析）ofthelightfromstarsandnebulae,particularlyforvolatile(挥发elements).B.Meteorites陨石(fornonvolatileelements).Meteoriteanalysesarenotasabundantowingtoalimitednumberofsamples.Table1-1

Atomicabundancesoftheelements(relativetosilicon=106atoms)

AtomicnumberElementCosmicChondrites球粒陨石）EarthEarth’scrust1H3.18×1010-8.4001.4×1052He2.21×1090.113.5×10-5-3Li49.5~50-2904Be0.810.69-315B3506.2-936C1.18×1072.0007.0001,7007N3.74×10690201408O2.15×1073.7×1063.5×1062.9×1069F2.450~7003003,30010Ne3.44×1060.001512×10-5-11Na6.0×1044.6×1044.6×1041.0×10512Mg1.061×1069.4×1058.9×1059.6×10413Al8.5×1046×1049.4×1043.0×10514Si1.00×1061.00×1061.00×1061.00×10615P9.6005.3001×1043,40016S5.0×1051.1×1051×10581017Cl5.7007003.20037018Ar1.172×1050.45.9×10-2-19K4.2003.5004,0005.3×10420Ca7.21×1044.9×1043.3×1041×10521Sc3529-4922Ti2.775~2.6002,0001.2×10423V262200-26024Cr1.27×1046.6008.00019025Mn9.3007.4004.0001,70026Fe8.3×1056.9×1051.35×1061×10527Co2.2101.3003.5004228Ni4.80×1044×1041×10513029Cu540250-8730Zn1.244130-11031Ga4812-2232Ge11520-2.133As6.64.6-2.434Se67.29-0.06335Br13.55-3.136Kr46.8-0.6×10-5-37Rb5.88~5-11038Sr26.920-43039Y4.83.4-3740Zr28~37-18041Nb1.41.0-2242Mo4.02.5-1.644Ru1.91.5--45Rh0.40.25--46Pd1.3~0.9--47Ag0.45~0.09-0.06548Cd1.480.079-0.1849In0.1890.001-0.08750Sn3.60.56-1.751Sb0.3160.11-0.1652Te6.420.60--53I1.090.051-0.3954Xe5.380.7×10-5-0.7×10-5-55Cs0.3856Ba4.85.05.031057Ka0.4450.390.392258Ce4359Or0.1460Bd0.780.640.641962Sm0.2263Eu0.0850.0820.0820.7964Gd0.2970.340.343.465Tb0.0550.0510.0510.5766Dy0.360.330.331.867Ho0.0790.0760.0760.7368Er0.269Tm0.0340.0310.0310.2870Yb0.271Lu0.0360.0310.0310.2972Hf71.773Ta0.0210.0160.0161.174W20.8275Re0.0530.0460.046-76Os0.750.540.54-77Ir0.7170.350.35-78Pt1.41.301.30-79Au0.200280Hg00.0481Tl0.1920.0010.0010.2282Pb83Bi0.1430.0020.0020.0890Th0.0580.0270.0274.192U0.02620.0090.0091.1B.RegularitiesanddifferencesoftheabundanceoftheelementsWhentherelativeabundancesofTable1-1areplottedagainstatomicnumber(Fig.1-1).Certainregularitiesanddifferencesareobserved.Anyattempttoexplaintheoriginoftheelementsmustexplainthefollowing.a.Theextremeabundanceofhydrogenandhelium(morethan99percentbyweightofallatoms).

b.Thegeneraldecreaseinabundancewithincreasingatomicnumber.c.Therelativelylowabundanceofsomeelements(suchaslithium,Beryllium,Boronandscandium)andtherelativelyhighabundanceofotherelements(suchasiron.nickel,andlead).d.Thegreaterabundanceofevenatomicnumberelementsascomparedtooddatomicnumberelements.

C.AbundanceoftheelementsintheEarth’sCrust

Whenwecomparetheabundanceoftheelementsintheearthwiththeirabundanceintheearth’scrust,acompletelydifferentsituationisfound(Table1-1).Theearthisahighlyfractionatedbodywithelementssuchaspotassiumstronglyconcentratedinthecrust.(A)Thefractionationoftheeartha.Thefractionation（分异作用）mayrepresenttheresultofheterogeneousaccretionfromacondensingsolarnebula,asdescribedearlier.b.Itmayrepresentsegregationwithinaninitiallyhomogeneousbody.Theinitiallysolidmassbecamemoltenowingtoheattoradioactivedecay.Moltendropsofironandotherheavymetalssanktothecore,andlightelementsmovedupwardtoformthecrust.Thebodythencooledandbecamesolid,withtheexceptionofpartofthecore.Thustheformationofthecore,mantle,andcrustmayhavebeentheresultofaccretion,withoutaliquidstage,oritmayhaveoccurredaspartofamoltenperiodafteraccretion.Ineithercase,furthersegregationofelementsintheuppermantleandinthecrustoccurredowingtomagmaformation.(B)Knowledgeonabundanceintheearthcrust

Ourknowledgeofthechemicalcompositionoftheearth’scrustcomesfromrockanalysesandfromgeophysicalevidenceonthestructureofthecrust.

Thegrosssubdivisions(亚层)usuallyconsideredare：a.Sedimentsandsedimentaryrocksatthesurfaceofthecrust;

b.Graniticmaterialintheupperpartofthecontinentalcrust（大陆地壳）;

c.Basalticmaterialinthelowerpartofthecontinentalcrustandmakinguptheoceaniccrust（洋壳）.Amajorproblemisuncertaintyaboutthecompositionandvolumeofeach.

(C)Someregularitiesa.Oxygenisthedominantelementinthecrust(about47percentbyweightand94percentbyvolume).Theothermajorelementissilicon,whichisabout28percentbyweight(butlessthan1percentbyvolumebecauseofthesmallsizeofthesiliconatom).

b.Ifwecompareabundancesofvariouselementsinchondrites(takenasrepresentativeofthemantle)

andinthecrust(Table1-1).Wefindthefollowingelementsstronglyenrichedinthecrust:H,Li,Be,F,Na,Al,K,Ti,Rb,Sr,Y,Zr,NbIn,Cs,BaLa,therareearths,Hf,Ta,W,Tl,Pb,Bi,Th,andU.(D)AbundanceoftheelementsintheOceanandtheAtmosphereThecompositionsofseawaterandtheearth’satmosphereareverydifferentfromthatoftheearth’ssolidmaterial(Tables1-2and1-3).

Therelativeproportionsofthemajorelements(Cl.Na,Mg,S,CaandK)inseawaterareconstant.Thoseelementsthatareinvolvedinbiologicalactivity(suchasC.O,N,andP)varyinconcentrationwithdepth,mainlybecausephotosynthesis（光合作用）canoccurnearthesurfacebutnotindeeperwater.

Only14elementoccurinseawaterwithaconcentrationover1partpermillion(ppm)byweight.Someoftheelementsthatoccurintraceamountsshowlargeregionalvariations,othersappeartohaveaconstantvalue.

Table1-2Compositionofseawater(inpartspermillionbyweight)AtomicnumberElementAbundanceAtomicnumberElementAbundance1H1.10×10534Se90×10-62He7.2×10-635Br67.33Li0.1736Kr0.21×10-34Be0.6×10-637Rb120×10-35B4.4538Sr8.16C2839Y3×10-66C(Inorganic)2.04041ZrNb26×10-615×10-67N(Dissolvedorganic)15.54247MoAg10×10-30.28×10-37N(DissolvedN2)0.674850CdSn0.11×10-30.81×10-38O(AsNO3-,NO2-,NH4+)6.0515354SbIXe0.33×10-364×10-347×10-68O(DissolveO2)8.83×1055556CsBa0.3×10-321×10-39F(AsH2O)1.35758LaCe2.9×10-61.3×10-610Ne120×10-659Pr0.64×10-611Na1.08×10460Nd2.3×10-612Mg1.29×10362Sm0.42×10-613Al1.0×10-363Eu0.114×10-614S2.964Gd0.6×10-615P0.08865Tb0.9×10-616S9.04×10266Dy0.73×10-617Cl1.94×10467Ho0.22×10-618Ar0.4568Er0.61×10-619K3.92×10269Tm0.13×10-620Ca4.11×10270Yb0.52×10-621Sc<4×10-671Lu0.12×10-622Ti1×10-372Hf<8×10-623V1.9×10-373Ta<2.5×10-624Cr0.2×10-374W<1.0×10-625Mn1.9×10-379Au11×10-626Fe3.4×10-380Hg0.15×10-327Co0.39×10-382Pb30×10-628Ni6.6×10-383Bi20×10-629Cu23×10-388Ra1×10-1630Zn11×10-390Th1.5×10-631Ga30×10-691Pa2×10-1332Ge60×10-692U3.3×10-333As2.6×10-3Table1-3Compositionoftheatmosphere(inpartspermillionbyweight)NameFormulaAbundanceNitrogenN2780,840OxygenO2209,460ArgonAr9,340CarbondioxideCO2330NeonNe18.18HeliumHe5.24MethaneCH42.0KryptonKr1.14HydrogenH20.5NitrousoxideN2O0.5SulfurdioxideSO20-1XenonXe0.087OzoneO3～0.05NitrogendioxideNO20-0.2AmmoniaNH30-traceCarbonmonoxideCO0-traceIodineI20-trace1.3GEOCHEMICALCLASSIFICATIONOFTHEELEMENTS(1)Goldschmidtideasa.

Goldschmidtpostulatedthatthethreemainphasesofmeteorites－－nativeiron,sulfide,andsilicate,alsorepresentedthemajorzonesoftheearth.Withtheearthhavinganoutersilicatelayer(andcrust)asulfide-oxidelayer,andanironcore.b.

Goldschmidtalsosuggestedthatthedistributionoftheelementsintheearthissimilartothatamongthemeteoritephases.

ChemicalanalysesofthethreephasesofmeteoritesbyGoldschmidtandotherinvestigatorsconfirmedhispredictionoftheassociationofthepreciousmetals（贵金属）withtheironphase.(2)Classificationoftheelements

In1922,Goldschmidtusedthetermssiderophile(亲铁),chalcophilc（亲铜）andlithophile（亲石）todescribeelementsconcentratedintheiron,sulfideandsilicatephasesrespectively.Healsousedthetermatmophile（亲气）forthoseelementsoccurringmainlyintheatmosphere.Studiesonmeteoritesandsmelterproductsallowedtheelementstobeassignedtothesegroups(Table1-3).

Goldschmidt’sclassificationisqualitativeonlyandcannotbeusedtoexplainmanyofthedetailsofelementoccurrenceanddistributioninthecrustoftheearth.Thegeneralvalidity（合理性）oftheclassificationisduetothesimilarityinelectronconfigurationofthevariousgroupsofelements.

Theseelementsarethosewhoseouter(valence)electronsundercertainchemicalconditionsarenotreadilyavailableforcombinationwithotherelements.Thustheytendtooccurinthenativestate.Theirelectronsarenotreadilyavailablebecausetheirelectronicstructureissuchthatthepositivechargeonthenucleuscanexertastrongpullontheouterelectrons.a.Siderophileelements

(亲铁元素)

Lithophileelementstendtoformmoreionicbondswithoxygenasinthesilicateminerals,thatiscombinewithoxygentoformoxide.However,theionsofthesetwogroupshavedifferentproperties(againbecauseofelectronicstructure).b.Lithophileelements

(亲石元素)

c.Chalcophileelements

(亲铜元素)

Chalcophileelementstendtoformcovalentbondswithsulfur.

Chalcophileelementshavevalenceelectronsthatareoutsideashellof18electrons.Therearegradationalchangesintheseelectronicpropertiesfromelement.Therearegradationalchangesintheseelectronicpropertiesfromelementtoelement;thussomeelementsshowastrongertendencytobelongtoagivengroupthandootherelements.

Anexampleismanganese（锰）,whichisbothlithophileandchalcophile.

Gold,forexample,ismoresiderophilethanmolybdenum.Similarlyoneelementmayshowatendencytobelongtotwogroups.GEOCHEMICALCLASSIFICATIONOFTHEELEMENTS

Chalcophile

LithophileAtmophileSiderophilemeteorites

crustCPFePSVSFeCoLiBeBOFHCNCoNiGeCrMnCuNiCuZnNaMgAlSiClOClBrMoRuRhZnAsSeGaAsSEKCaScTiVIPdSnTaAgCdTeMoRhPdCrMnBrRbSrReOsIrAgCdInYZrNbICsPtAuSbTEHgBaLaHfTaWTlPbBiThURareearthsFishman’sClassificationFishman’sclassificationisbasedonthedifferencesofnatureandradiusofionsamong,andcoexistenceofelementsingeologyandmineralizationgenesis.AnditisalsoatransformationoftheMendeleev’speriodicaltableofelements.Table1-4TableofFishman’sClassification

族列ⅠⅡⅢⅣⅤⅥⅦ0ⅠⅡⅢⅣⅤⅥⅦⅧ列12b3b———————BAl—CSi—NP—OSHFClHeNeArLiNaKBeMgCa——Sc——Ti——V——Cr——Mn——Fe、Co、Ni2a3a4579CuAgAuZnCdHgGaInTlGeSnPbAsSbBiSeTePoBrI?KrXeRnRbCs?SrBaRaYTRAcZrHfThNbTaPaMoWUTcRe—Ru、Rh、PdOs、Ir、Pt6810AccordingtoFishman’sclassification,asweseeinTable1-6,elementscanbedividedintothreegroups.Ineachgroup,whichFishmancallafield（场）,geochemicalpropertiesofelementsaresimilartoeachother,anddistinguishedwiththoseofotherfields.(1)CommonField（普通场）ElementsinthisfieldarelistedintheuphalfoftheMendeleev’speriodicaltableofelementswiththeiratomicnumberfrom1(Hydrogen)to28(Nickel).Theywidelydistributedintheearthcrustandthemainelementsmakingofthelithosphere（岩石圈）,thehydrosphere（水圈）andtheatmosphere（大气圈）.(2)SulfideField（硫化物场）ElementsinthedownleftcornerofTable1-6areinthisfield.Sulfidefieldelementshavehighpotentialtocombinewithsulfurtoformsulfides,andwithotherelementsinthecolumnwhichsulfurin,suchasSeandTetoformtheirstablecompounds.(3)AcidField（酸性场）AcidfiledislocatedinthedownrightcornerofTable1-6.Elementslistedontheleftsideofthefieldarealkalimetalsandalkaline-earthmetals.1.2.3Chavalizk’sClassificationTakingthenatureofcoexistenceofelementsinrocksandminerals,Chavalizkidevelopedaclassificationbasedontherelationshipbetweenelements’geochemistryandtheirelectronshellstructuresandcrystalchemistryproperties.Thereare12groups(族)ofelementsinChavalizki’sclassification.(1)Hydrogen:H(2)Mainrock-formingelements（造岩元素）:Li,Be,Na,Mg,Al,Si,K,Ca,Rb,Sr,CsandBa(3)Inertgaseselements:He,Ne,Ar,Kr,Xe,Rn(4)Mineralizer（矿化剂）

orpneumatolyte（气成）

elements:B,C,N,O,F,P,S,Cl(5)Irongroupelements:Se,Ti,V,Cr,Mn,Fe,Co,Ni(6)Raremetalelements:TR(includingY),Zr,Hf,Nb,Ta,etc.(7)Radioelements:fromFr(87)toU(92),mostofattentionshouldbepaidonresearchingRa,ThandU(8)Tungstenandmolybdenumgroupelements:Mo,W,Te,Re(9)Platinumgroupelements:Ru,Rh,Pd,Os,Tr,Pt(10)Typicalmineralizationelementsofsulfidedeposits:Cu,Zn,Ga,Ge,Ag,Cd,In,Sn,Au,Hg,Tl,Pb(11)Semimetal(半金属)andheavymineralizerelements:AsSb,Bi,Se,Te(12)Heavyhalogenelements:BrandISUMMARY1.Themostabundantelementsintheuniversearehydrogenandhelium.Alltheotherelementsprobablyformedbynuclearreactions(instars)involvingthesetwosimpleelements.2.Oursuniscomposedmostlyofhydrogenandhelium,andthecompositionofotherbodiesinthesolarsystemhasbeengovernedbytheirmodeoforigin,particularlytheextentoftheirlossofvolatileelements.3.Thematerialsofgreatestinterestingeochemistrytheearth’scrust,oceans,andatmosphere,representextremefractionationoftheprimordial（原始）materialfromwhichtheearthwasformed.Thisfractionationhasbeen,andis,governedbychemicalenvironmentandbythechemicalpropertiesoftheelements,whichcanbeusedtoexplainGoldschmidt’sempiricalgeochemicalclassificationoftheelements.

QUESTIONS

1.Usingtheperiodictable,nametwotrace(low-abundance)elementsthatyoumightexpecttosubstituteforsulfurinnature.Checkyouranswerbylookingatsomegeochemistryreferences.2.Certainpairsofelementshaveverysimilarchemicalandgeochemicalproperties.ForeachelementincolumnAmatchanelementfromcolumnBthathassimilarproperties.NotethatnotalltheelementsincolumnBwillbeusedsincethereareextraelementslistedthere.

ColumnAColumnBa.Niobium（铌）1.Aluminumb.Strontium2.Ironc.Hafnium（铪）3.Calciumd.Gallium4.Sulfure.Rubidium5.Tantalum（钽）

6.Palladium（钯）

7.Potassium8.Zirconium

3.Whichelementineachofthefollowingpairswouldyouguessismoreabundantintheearth’scrust?a.Copperorvanadium.b.Bariumorcobalt.c.Neodymium（钕）ortungsten.d.Mercuryorthallium（铊）.e.Silverorcesium4.Usingtheabundancesofchlorine（1.94×104）andsilicon（2.9）inpartspermillionbyweightconvertthevalueforchlorineinseawaterfrompartspermillionbyweighttoatomicabundanceintermsofSi=106atoms.Chapter2.THERMODYNAMICS

（热力学）2.1BASICCONCEPTSANDTERMS

Whenapplyingthermodynamicstogeologicorotherproblemsthematerialofinterestisreferredtoasthesystemandthematerialaroundthesystemasthesurroundings.A.

SystemandSurrounding（体系和环境）

Systemisdefinedaspartoftheuniversethatisseparatedfromtherestbydefiniteboundaries.Itmaycontaingases,liquidsorsolids,oranycombinationofthese.

Surroundingisthematerialaroundthesystem.B.Phase（相）

Phaseisdefinedasaphysicallyhomogeneousportionofasystemwithadefiniteboundary.Itisalsodescribletospecifythechemicalcompositionofthesystemofinterest.Thisisdonebylistingtheamountsofthecomponents(chemicalconstituents)ofthesystem.C.Equationofstate（状态方程）

Anequationthatrelatescertainpropertiesofasystemiscalled(equationofstate).Thenumberofconstituents（组分数）:Thesmallestnumberneededtodescribeallvariationsinthecompositionofeveryphase.e.g.thenumberofcomponentsofthesystemgypsum-anhydrite-wateristwo,CaSO4andH2O,sincegypsumcanbedescribedbyccombinationofthesetwocomponents.CaSO4.H2O＝CaSO4+H2OD.Energy（能）

Energyisthecapacitytodoworkfromthefieldofmechanics.E.Work（功）

Inmechanics,workisdefinedastheresultofaforceactingthroughadisplacement.Workdoneonabodythatdisplacestheentirebody,suchasliftingitoracceleratingit,producesanincreaseintheenergyofthebody,ifthebodyislifted,thereisanincreaseinitspotentialenergy.F.Thermodynamics（热力学）

Thermodynamicsisconcernedwiththeinternalenergyofabodyorsystem.

Thuschangesthattakeplacewithinasystem,owingtointeractionofthesystemanditssurroundings,aresaidtocauseachangeinitsinternalenergy（内能）.

Theconceptofequilibriumcanbeappliedtodifferentphasesthatdonotreactchemically(physicalequilibrium)ortodifferentsubstancesthatarereactingwitheachother(chemicalequilibrium).Simplystated,asysteminequilibriumdoesnotchangewithtime.

ThusinthechemicalequilibriumA+BC+D(2-1)AandBmaybecontinuouslyreactingtoformCandD，butCandDarealsocontinuouslyreactingtofromAandB.Atequilibriumthereisaconstantamountofeachsubstance.

Metastable

state（亚稳态）:Whenasubstanceoccursinaformthatisnotthemoststableformundertheexistingconditions,butdoesnotspontaneously(自动)changetoamorestableformitissaidtobeinametastablestate.

Oftenthisconditionisduetoaveryslowrateofreaction.Givenenoughtime,themoststableformwilldevelop.2.2FIRSTLAWOFTHERMODYNAMICS

（热力学第一定律）(1)Lawofconservationofenergya.Inmechanicalsystemscharacterizedbykineticandpotentialenergy,thetotalenergyofasystemisconstant.

Thisrelationshipiscalledtheprincipleorlawofconservationofenergy.TheexperimentalworkofphysicistJ.P.Jouleduringtheperiod1840-1849ontherelationbetweenheatflowandworkdoneledscientiststoapplytheprincipleofconservationofenergytothermodynamicprocesses.Theimportantresultofthisexperimentalworkwastoshowthattheamountofworkrequiredtoraisethetemperatureofasystemthroughagivenrangeisindependentofthetypeofworkdone.Foranadiabatic(绝热的)system(noheatflowinoroutofthesystem),theamountofworkdoneonthesystemisequaltothechangeininternalenergy.

b.Thestatementofequivalence（等值）ofinternalenergychangewithworkdoneplusheattransferredisknownasthefirstlawofthermodynamics.Therelationshipholdstrueinallcaseswhereithasbeentestedexperimentallyortheoretically.Mathematically,wecanstatethefirstlawas

dU=dQ-dW(infinitesimal无限小change)and

U=Q-W(finitechange)(3-2)whereUisthechangeininternalenergy.Qisheattransferred,

andWisworkdone.

Thusthereisanincreaseininternalenergyinchangingaragonite（文石）tocalcite.Practicallyallthechangeisduetoabsorptionofheatbythesystem.At25Cand1atmospherepressure,thechangefromaragonitetocalcitecanoccurmuchmoreeasilythanthechangefromgraphitetodiamond.Studiesofthesematerialsinnatureconfirmthisconclusion.Calciteisoftenfoundasapseudomorph（假象）afteraragonite.Whereassucharelationshipisnotfoundforgraphiteanddiamond.Ourresultsshowthatalmost400caloriespermolemoreenergyisrequiredtochangegraphitetodiamondthanisrequiredtochangearagonitetocalcite.Furthermoretheamountofenergyneededtochangearagonite（文石）tocalciteisrelativelysmall.Ithasbeenfoundthattheinternalenergyismostusefulinstudyingchangesthattakeplaceatconstantvolume.Inthesecasestheinternalenergychangeisequaltotheheatflow.

However,chemicalreactionsandphasechangesmoreoftenoccurunderconstantpressureconditions.Thusitwouldbeusefultohaveanothercharacteristicofasystem,inadditiontoU,thatisequaltotheheatflowwhenpressureisconstant.

(2)Enthalpy（焓）WedefinethisnewfunctionasH=U+PV;ThefunctionHiscalledtheenthalpy（焓）.Asinthecaseoftheinternalenergyonlychangesinenthalpycanbemeasured.ThesechangescanbeexpressedasdH=dU+PdV+VdP

Usingequation(3-2),whenPVworkisperformed

dH=dQ-PdV+PdV+VdP(dU=dQ-dW)=dQ+VdP(infinitesimalchange)or

H=Q+VP(finitechange)(3-5)NotethatH=Qwhenthepressureisconstant.TABLE2-2STANDARDHEATSOFFORMATION,ENTROPLES,ANDFREEENERGIESOFFORMATIONAT298.15K(25C)TABLE2-2STANDARDHEATSOFFORMATION,ENTROPLES,ANDFREEENERGIESOFFORMATIONAT298.15K(25C)

2.3

ENTROPY(熵)ANDTHESECONDLAWOFTHERMODYNAMICSEntropydealswithincreasingdegreeofdisorderinasystem.（熵是体系无序程度增加的一种度量）

THESECONDLAWOFTHERMODYNAMICS:dS=dQ/T

Whatmakesachemicalreactionoccur?Wehavealreadydiscussedtheheatchangeinvolvedinareaction.Itwasoncethoughtthatthedifferenceininternalenergyrepresentedbythisflowisthecauseofchemicalreaction,formostchemicalreactionsresultinthereleaseofheat.Thuswecouldreasonthatreactionsoccurwhenadecreaseintheinternalenergyofthesystembeingconsideredispossible,thisdecreaseoccurringbythereleaseofheatfromthesystem.

A.Achemicalreactionwouldnotoccurifitwouldresultinanabsorptionofheat.

B.Alargenumberofnaturalprocesses,wefindthatingeneralspontaneousprocessesinnaturetendtowardtheformationoflessordered(ororganized)structures.Rockstendtofallapartandmineralstendtodissolveatthesurfaceoftheearth.Vegetationdecayswhenitdiesandcannolongermakeuseofenergyfromthesun.

C.Athermodynamicfunctionthattakesintoaccountbothheatflowanddegreeofordering.(2)Reactionsthatgiveoffheatandpr