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1、CHAPTER3EnergyBalances:Thermodynamics–KineticsThecrystalstructureandchemicalcompositionofpureandinterstrati?edclayspeciesbeingfamiliar(seeChaps.1and2),itispossiblenowtoinvestigateamoresubtleconsequence:thedistributionofenergyinsidethecrystallatticeanditsin
2、nerandoutersurfaces.Indeed,ifthisisunderstood,thenitbe-comespossibletorelatethecrystallochemicalcharacteristicsofclaymineralstothephysicochemicalconditionsprevailingduringtheirformation.Thisisafascinatingperspectiveforchemists,mineralogistsandgeologistswho
3、,fordifferentbutconvergingreasons,dealwithmineralreactionsinclaymaterials.Particularly,thismakesitpossibletostudytheeffectsformoreorlesslongperiodsoftimeofchemicalinteractionsinhumanenvironments(pollution,cropping,wastestorageetc).3.1ThermodynamicsofEquili
4、brium3.1.1IntroductionThecharacterisationofaclay,orofanyothermineralspecies,requiresthedeterminationofitstridimensionalstructureandchemicalcomposition.Thisamountstoaspacerepresentationofallthechemicalbonds?xingcationsandanionsinacrystallatticewhosesmallest
5、entityisthecrystalunitcell.Eachtypeofbond(positionoftheioninthestructure)ischaracterisedbyapotentialenergy.Eachionvibratingoroscillatingaboutthispositionaddsakineticenergy.Thesumofthepotentialandkineticenergiesformtheenthalpy(H)ofthecrystal.Entropy(S)isapa
6、rameterthatdescribesquantitativelythedegreeofinternaldisorderofasubstance.Vapourhasahigherentropythanwater,whichitselfhasahigherentropythanice.Thisconceptisveryimportantbecauseitpermitsde?nitionofthemajorparametercontrollingchemicalreactions:freeenergy(G):
7、Gcryst=Hcryst?TScryst(3.1)Enthalpyandentropyincreasewiththemassorvolumeofthecrystal;theyareextensivevariables.Theyareexpressedinrelationtothe“molecule”rep-108EnergyBalances:Thermodynamics–KineticsFig.3.1.Respectivedomains)ofthermodynamicsandGkineticstransi
8、torystategy(enerEakineticsGrinitialstate(reactants)?GthermodynamicsGpfinalstate(products)degreeofreactionprogressresentativeofthecrystal,namelythecrystalunitcell:HinJmol?1andSinJK?1mol?1.The?rstlawofthermodyn
