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1、11.HYDROGENFUNDAMENTALS1.1.INTRODUCTIONHydrogenisthefirstelementintheperiodictablewiththeatomicnumber1.Itisthelightestandmostabundantelementintheuniverserepresenting75mass%or90vol%ofallmatter.OnEarth,itismostlyfoundincompoundswithalmosteveryotherelement.Consi
2、deringjustthecompoundwater,14thehydrogencontentsboundinthetotalwatersupplyoftheworldisontheorderof10t.Hydrogenexistsalsoasafreeelementintheatmosphere,butonlytotheextentoflessthan1ppm(byvolume).Freeionichydrogenismorereactivethanmolecularhydrogen,thenonpolar-c
3、ovalentcompoundoftwohydrogenatoms.In1776,byHenryCavendishidentifiedhydrogenasadistinctspecies.Itwasgiventhename“watermaker”byAntoineLavoisiersevenyearslater,whoprovedthatwaterwascomposedofhydrogenandoxygen.Themostcommonhydrogenisotopeisprotium(H-1,H,atomicmas
4、s1.007822).Thesecondisotopeisthestabledeuterium(H-2,D)orheavyhydrogendiscoveredin1932byH.C.Ureyandco-workers.Deuteriumhasanaturalfractionof0.014%withphysicalandchemicalpropertiesslightlydifferentfromH-1.NearlyallDinnaturalhydrogenisincombinationwithhydrogenat
5、oms,thediatomicHDwithafractionof0.032%innaturalhydrogen;theexistenceofmolecularDishighlyimprobable.Thirdhydrogenisotopeistheradioactivetritium(H-3,T)withahalflifeof12.3years,discoveredin1934byE.Rutherford.Butalsotheshort-livedisotopesH-4,H-5,andH-7havebeensyn
6、thesizedinthemeantime.1.2.PHYSICALPROPERTIESOFHYDROGENHydrogencanbeconsideredanidealgasoverawidetemperaturerangeandevenathighpressures.Atstandardtemperatureandpressureconditions,itisacolourless,odourless,tasteless,non-toxic,non-corrosive,non-metallicdiatomicg
7、as,whichisinprinciplephysiologicallynotdangerous.Oneofitsmostimportantcharacteristicsisitslowdensity,whichmakesitnecessaryforanypracticalapplicationstoeithercompressthehydrogenorliquefyit.Itispositivelybuoyantaboveatemperatureof22K,i.e.,over(almost)thewholete
8、mperaturerangeofitsgaseousstate.Fig.1-1:Phasediagramofhydrogen2Hydrogengasishighlydiffusiveandhighlybuoyant;itrapidlymixeswiththeambientairuponrelease.Thediffusionvelocityisproportionalto
