Enthalpy of vaporization - Wikipedia

The enthalpy of vaporization (symbol ∆Hvap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) ... Enthalpyofvaporization FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch Energytoconvertaliquidsubstancetoagas;afunctionofpressure Thisarticleincludesalistofgeneralreferences,butitlackssufficientcorrespondinginlinecitations.Pleasehelptoimprovethisarticlebyintroducingmoreprecisecitations.(March2016)(Learnhowandwhentoremovethistemplatemessage) Temperature-dependencyoftheheatsofvaporizationforwater,methanol,benzene,andacetone Theenthalpyofvaporization(symbol∆Hvap),alsoknownasthe(latent)heatofvaporizationorheatofevaporation,istheamountofenergy(enthalpy)thatmustbeaddedtoaliquidsubstancetotransformaquantityofthatsubstanceintoagas.Theenthalpyofvaporizationisafunctionofthepressureatwhichthattransformationtakesplace. Theenthalpyofvaporizationisoftenquotedforthenormalboilingtemperatureofthesubstance.Althoughtabulatedvaluesareusuallycorrectedto298 K,thatcorrectionisoftensmallerthantheuncertaintyinthemeasuredvalue. Theheatofvaporizationistemperature-dependent,thoughaconstantheatofvaporizationcanbeassumedforsmalltemperaturerangesandforreducedtemperature T r {\displaystyleT_{r}} ≪ 1 {\displaystyle{}\ll1} .Theheatofvaporizationdiminisheswithincreasingtemperatureanditvanishescompletelyatacertainpointcalledthecriticaltemperature( T r = 1 {\displaystyleT_{r}=1} ).Abovethecriticaltemperature,theliquidandvaporphasesareindistinguishable,andthesubstanceiscalledasupercriticalfluid. Contents 1Units 2Enthalpyofcondensation 3Thermodynamicbackground 4Vaporizationenthalpyofelectrolytesolutions 5Selectedvalues 5.1Elements 5.2Othercommonsubstances 6Seealso 7References Units[edit] ValuesareusuallyquotedinJ/mol,orkJ/mol(molarenthalpyofvaporization),althoughkJ/kg,orJ/g(specificheatofvaporization),andolderunitslikekcal/mol,cal/gandBtu/lbaresometimesstillusedamongothers. Enthalpyofcondensation[edit] Theenthalpyofcondensation(orheatofcondensation)isbydefinitionequaltotheenthalpyofvaporizationwiththeoppositesign:enthalpychangesofvaporizationarealwayspositive(heatisabsorbedbythesubstance),whereasenthalpychangesofcondensationarealwaysnegative(heatisreleasedbythesubstance). Thermodynamicbackground[edit] Molarenthalpyofzincabove298.15 Kandat1 atmpressure,showingdiscontinuitiesatthemeltingandboilingpoints.Theenthalpyofmelting(ΔH°m)ofzincis7323 J/mol,andtheenthalpyofvaporization(ΔH°v)is115330 J/mol. Theenthalpyofvaporizationcanbewrittenas Δ H vap = Δ U vap + p Δ V {\displaystyle\DeltaH_{\text{vap}}=\DeltaU_{\text{vap}}+p\,\DeltaV} Itisequaltotheincreasedinternalenergyofthevaporphasecomparedwiththeliquidphase,plustheworkdoneagainstambientpressure.Theincreaseintheinternalenergycanbeviewedastheenergyrequiredtoovercometheintermolecularinteractionsintheliquid(orsolid,inthecaseofsublimation).Henceheliumhasaparticularlylowenthalpyofvaporization,0.0845 kJ/mol,asthevanderWaalsforcesbetweenheliumatomsareparticularlyweak.Ontheotherhand,themoleculesinliquidwaterareheldtogetherbyrelativelystronghydrogenbonds,anditsenthalpyofvaporization,40.65 kJ/mol,ismorethanfivetimestheenergyrequiredtoheatthesamequantityofwaterfrom0 °Cto100 °C(cp =75.3 J/K·mol).Caremustbetaken,however,whenusingenthalpiesofvaporizationtomeasurethestrengthofintermolecularforces,astheseforcesmaypersisttoanextentinthegasphase(asisthecasewithhydrogenfluoride),andsothecalculatedvalueofthebondstrengthwillbetoolow.Thisisparticularlytrueofmetals,whichoftenformcovalentlybondedmoleculesinthegasphase:inthesecases,theenthalpyofatomizationmustbeusedtoobtainatruevalueofthebondenergy. Analternativedescriptionistoviewtheenthalpyofcondensationastheheatwhichmustbereleasedtothesurroundingstocompensateforthedropinentropywhenagascondensestoaliquid.Astheliquidandgasareinequilibriumattheboilingpoint(Tb),ΔvG = 0,whichleadsto: Δ v S = S gas − S liquid = Δ v H T b {\displaystyle\Delta_{\text{v}}S=S_{\text{gas}}-S_{\text{liquid}}={\frac{\Delta_{\text{v}}H}{T_{\text{b}}}}} Asneitherentropynorenthalpyvarygreatlywithtemperature,itisnormaltousethetabulatedstandardvalueswithoutanycorrectionforthedifferenceintemperaturefrom298 K.Acorrectionmustbemadeifthepressureisdifferentfrom100 kPa,astheentropyofagasisproportionaltoitspressure(or,moreprecisely,toitsfugacity):theentropiesofliquidsvarylittlewithpressure,asthecompressibilityofaliquidissmall. Thesetwodefinitionsareequivalent:theboilingpointisthetemperatureatwhichtheincreasedentropyofthegasphaseovercomestheintermolecularforces.Asagivenquantityofmatteralwayshasahigherentropyinthegasphasethaninacondensedphase( Δ v S {\displaystyle\Delta_{\text{v}}S} isalwayspositive),andfrom Δ G = Δ H − T Δ S {\displaystyle\DeltaG=\DeltaH-T\DeltaS} , theGibbsfreeenergychangefallswithincreasingtemperature:gasesarefavoredathighertemperatures,asisobservedinpractice. Vaporizationenthalpyofelectrolytesolutions[edit] Estimationoftheenthalpyofvaporizationofelectrolytesolutionscanbesimplycarriedoutusingequationsbasedonthechemicalthermodynamicmodels,suchasPitzermodel[1]orTCPCmodel.[2] Selectedvalues[edit] Thissectionneedsadditionalcitationsforverification.Pleasehelpimprovethisarticlebyaddingcitationstoreliablesources.Unsourcedmaterialmaybechallengedandremoved.(September2018)(Learnhowandwhentoremovethistemplatemessage) Elements[edit] vteEnthalpiesofvaporizationoftheelements 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Group → ↓ Period 1 H0.44936 He0.0845 2 Li145.92 Be292.40 B489.7 C355.8 N2.7928 O3.4099 F3.2698 Ne1.7326 3 Na96.96 Mg127.4 Al293.4 Si300 P12.129 S1.7175 Cl10.2 Ar6.447 4 K79.87 Ca153.6 Sc314.2 Ti421 V452 Cr344.3 Mn226 Fe349.6 Co376.5 Ni370.4 Cu300.3 Zn115.3 Ga258.7 Ge330.9 As34.76 Se26.3 Br15.438 Kr9.029 5 Rb72.216 Sr144 Y363 Zr581.6 Nb696.6 Mo598 Tc660 Ru595 Rh493 Pd357 Ag250.58 Cd100 In231.5 Sn295.8 Sb77.14 Te52.55 I20.752 Xe12.636 6 Cs67.74 Ba142 Lun/a Hf575 Ta743 W824 Re715 Os627.6 Ir604 Pt510 Au334.4 Hg59.229 Tl164.1 Pb177.7 Bi104.8 Po60.1 At27.2 Rn16.4 7 Frn/a Ra37 Lrn/a Rfn/a Dbn/a Sgn/a Bhn/a Hsn/a Mtn/a Dsn/a Rgn/a Cnn/a Nhn/a Fln/a Mcn/a Lvn/a Tsn/a Ogn/a La414 Ce414 Prn/a Ndn/a Pmn/a Smn/a Eun/a Gdn/a Tbn/a Dyn/a Hon/a Ern/a Tmn/a Ybn/a Acn/a Th514.4 Pan/a Un/a Npn/a Pun/a Amn/a Cmn/a Bkn/a Cfn/a Esn/a Fmn/a Mdn/a Non/a   EnthalpyinkJ/mol,measuredattheirrespectivenormalboilingpoints 0–10kJ/mol 10–100kJ/mol 100–300kJ/mol >300kJ/mol Thevaporizationofmetalsisakeystepinmetalvaporsynthesis,whichexploitstheincreasedreactivityofmetalatomsorsmallparticlesrelativetothebulkelements. Othercommonsubstances[edit] Enthalpiesofvaporizationofcommonsubstances,measuredattheirrespectivestandardboilingpoints: Compound Boilingpoint,atnormalpressure Heatofvaporization (K) (°C) (°F) (J/mol) (J/g) Acetone 329 56 133 31300 538.9 Aluminium 2792 2519 4566 294000 10500 Ammonia 240 −33.34 −28 23350 1371 Butane 272–274 −1 30–34 21000 320 Diethylether 307.8 34.6 94.3 26170 353.1 Ethanol 352 78.37 173 38600 841 Hydrogen(parahydrogen) 20.271 −252.879 −423.182 899.2 446.1 Iron 3134 2862 5182 340000 6090 Isopropylalcohol 356 82.6 181 44000 732.2 Methane 112 −161 −259 8170 480.6 Methanol 338 64.7 148 35200[3] 1104 Propane 231 −42 −44 15700 356 Phosphine 185 −87.7 −126 14600 429.4 Water 373.15 100 212 40660 2257 Seealso[edit] Clausius–Clapeyronrelation Shimanskyequation,describesthetemperaturedependenceoftheheatofvaporization Enthalpyoffusion,specificheatofmelting Enthalpyofsublimation Jobackmethod,estimationoftheheatofvaporizationatthenormalboilingpointfrommolecularstructures Latentheat References[edit] ^Ge,Xinlei;Wang,Xidong(20May2009)."EstimationofFreezingPointDepression,BoilingPointElevation,andVaporizationEnthalpiesofElectrolyteSolutions".Industrial&EngineeringChemistryResearch.48(10):5123.doi:10.1021/ie900434h. ^Ge,Xinlei;Wang,Xidong(2009)."CalculationsofFreezingPointDepression,BoilingPointElevation,VaporPressureandEnthalpiesofVaporizationofElectrolyteSolutionsbyaModifiedThree-CharacteristicParameterCorrelationModel".JournalofSolutionChemistry.38(9):1097–1117.doi:10.1007/s10953-009-9433-0.ISSN 0095-9782.S2CID 96186176. ^NIST CODATAKeyValuesforThermodynamics Gmelin,Leopold(1985).Gmelin-HandbuchderanorganischenChemie/08a(8.,völligneubearb.Aufl. ed.).Berlin[u.a.]:Springer.pp. 116–117.ISBN 978-3-540-93516-2. NISTChemistryWebBook Young,FrancisW.Sears,MarkW.Zemansky,HughD.(1982).Universityphysics(6th ed.).Reading,Mass.:Addison-Wesley.ISBN 978-0-201-07199-3. vteStatesofmatter(list)State Solid Liquid Gas/Vapor Plasma Lowenergy Bose–Einsteincondensate Fermioniccondensate Degeneratematter QuantumHall Rydbergmatter Rydbergpolaron Strangematter Superfluid Supersolid Photonicmolecule Highenergy QCDmatter LatticeQCD Quark–gluonplasma Color-glasscondensate Supercriticalfluid Otherstates Colloid Glass Crystal Liquidcrystal Timecrystal Quantumspinliquid Exoticmatter Programmablematter Darkmatter Antimatter Magneticallyordered Antiferromagnet Ferrimagnet Ferromagnet String-netliquid Superglass Transitions Boiling Boilingpoint Condensation Criticalline Criticalpoint Crystallization Deposition Evaporation Flashevaporation Freezing Chemicalionization Ionization Lambdapoint Melting Meltingpoint Recombination Regelation Saturatedfluid Sublimation Supercooling Triplepoint Vaporization Vitrification Quantities Enthalpyoffusion Enthalpyofsublimation Enthalpyofvaporization Latentheat Latentinternalenergy Trouton'srule Volatility Concepts Baryonicmatter Binodal Compressedfluid Coolingcurve Equationofstate Leidenfrosteffect Macroscopicquantumphenomena Mpembaeffect Orderanddisorder(physics) Spinodal Superconductivity Superheatedvapor Superheating Thermo-dielectriceffect AuthoritycontrolNationallibraries France(data) Germany Israel UnitedStates Other FacetedApplicationofSubjectTerminology Retrievedfrom"https://en.wikipedia.org/w/index.php?title=Enthalpy_of_vaporization&oldid=1085441590" Categories:EnthalpyHiddencategories:ArticleswithshortdescriptionShortdescriptionmatchesWikidataUseAmericanEnglishfromMarch2019AllWikipediaarticleswritteninAmericanEnglishUsedmydatesfromOctober2014Articleslackingin-textcitationsfromMarch2016Allarticleslackingin-textcitationsArticlesneedingadditionalreferencesfromSeptember2018AllarticlesneedingadditionalreferencesArticleswithBNFidentifiersArticleswithGNDidentifiersArticleswithJ9UidentifiersArticleswithLCCNidentifiersArticleswithFASTidentifiers Navigationmenu Personaltools NotloggedinTalkContributionsCreateaccountLogin Namespaces ArticleTalk English Views ReadEditViewhistory More Search Navigation MainpageContentsCurrenteventsRandomarticleAboutWikipediaContactusDonate Contribute HelpLearntoeditCommunityportalRecentchangesUploadfile Tools WhatlinkshereRelatedchangesUploadfileSpecialpagesPermanentlinkPageinformationCitethispageWikidataitem Print/export DownloadasPDFPrintableversion Inotherprojects WikimediaCommons Languages AfrikaansالعربيةAragonésAsturianuБългарскиBosanskiCatalàЧӑвашлаČeštinaDanskDeutschEestiEspañolEsperantoEuskaraفارسیFrançaisGalego한국어हिन्दीHrvatskiBahasaIndonesiaItalianoעבריתJawaქართულიҚазақшаLietuviųLa.lojban.MagyarМакедонскиBahasaMelayuNederlands日本語NorskbokmålNorsknynorskOʻzbekcha/ўзбекчаPolskiPortuguêsRomânăРусскийScotsසිංහලSimpleEnglishSlovenčinaSlovenščinaСрпски/srpskiSrpskohrvatski/српскохрватскиSuomiSvenskaதமிழ்ไทยTürkçeУкраїнськаاردوTiếngViệt吴语中文 Editlinks