AquaticChemicalKinetics-UniversityofVermont：水化学动力学-佛蒙特大学

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1、MetastabilityandstabilityWhydometastablephasesform?Ostwald’sStepRule:Thefirstsolidphasetoprecipitateismostsolublephase(i.e.theleaststable,ormetastable,phase)WilhelmOstwald(1853–1932)AragoniteinsteadofcalciteSiO2.x(H2O)insteadofquartzFeSinsteadofpyriteFerrihydriteinsteadofhematiteCla

2、ssicalNucleationTheoryThenucleusincreasesinGibb’sfreeenergyasitaccretesThesizereachesacriticalvalueThefreeenergydecreaseswithsizeuntilanegativevalueisreached(i.e.amorestablephase)e.g.waterat0oC,criticalradiusis8Åwithca.90H2OmoleculesClassicalNucleationtheoryandtheOstwaldStepRuleG=

3、Gbulk+GsurfaceThefreeenergyrequiredtomakeanucleusisthesumofthefreeenergygainedinmakingbondsplusthefreeenergyrequiredtomakeasurface.Gsurface=4r2Whereistheinterfacialenergyorinterfacialsurfacetension.TheinterfacialfreeenergyincreaseswithdecreasingsolubilityThereforethemoresoluble

4、,leaststablephaseformsfirstbecauseithasthelowerinterfacialenergy.GeochemicalKineticsLookat3levelsofchemicalchange:PhenomenologicalorobservationalMeasurementofreactionratesandinterpretationofdataintermsofratelawsbasedonmassactionMechanisticElucidationofreactionmechanisms=the‘elementa

5、ry’stepsdescribingpartsofareactionsequence(orpathway)StatisticalMechanicalConcernedwiththedetailsofmechanismsenergeticsofmolecularapproach,transitionstates,andbondbreaking/formationNonequilibriumEquilibrium=DEATHforallorganismsWhy?availablemetabolicenergy:DGR=DG0+RTlnQBiogenic,atmo

6、sphericelements(C,N,P,S,O)areinnonequilibriuminnaturalwatersTherearethousandsofnaturalorganicmoleculesandevenmoresyntheticonesthatarenotthermodynamicallystableinthepresenceofO2BlackSmokersLifethriveshereontheH2SandFe2+comingoutoftheventsH2SandFe2+isderivedfrominteractionofhot(350-40

7、0+ºC)fluidinteractingwithbasaltsWhatelseaffectsdisequilibrium?Physicalforces–gasrising,convectioncells,particlesettling,transportBiologicalactivitysegregatesredoxspeciesMineralreactionsaffectotherreactions,perturbingredoxequilibriaHowlongitlasts,theforcesthatmaintainitdescribedbyki

8、neticsTimeScalesRea