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1、化学专业英语马永祥翻译课 作者： 日期：36沸点和蒸馏BoilingPointsofPureLiquids沸点的纯液体Anygivenliquid,whenadmittedintoaclosedevacuatedspace,evaporatesuntilthevaporattains acertaindefinitepressure,whichdependsonlyuponthetemperature.Thispressure,whichisthepressureexertedbythevaporinequilibriumwiththeliquid,isthevaporpressureofth
2、eliquidatthattemperature.Asthetemperatureincreases.thevaporpressureofatypicalliquidxincreasesregularlyasshownbythegeneralizedvaporpressure-temperaturecurveBC,inFig.5.任何给定的液体,当进入一个封闭的疏散空间,蒸发到蒸汽形成某种明确的压力,仅仅依赖于温度。这种压力,这是由蒸汽压力与液体平衡的,是液体的蒸气压在温度。随着温度的升高。这个压力，是通过在与液体平衡的蒸汽施加的压力，是液体在该温度下的蒸汽压，其随着温度的增加而增加。一个典型
3、液体x的蒸汽压的增加经常如图五所示，广义蒸汽压-温度曲线BC。Atthetemperature,Tp,wherethevaporpressurereaches101.3kPa.xbeginstoboilandTpiscalledtheNORMALBOILINGPOINTofx.Everyliquidwhichdoesnotdecomposebeforeitsvaporpressurereaches101.3kPa.hasitsowncharacteristicboilingpoint.Ingeneral,theboilingpointofasubstancedependsuponthemass
4、ofitsmoleculesandthestrengthoftheattractiveforcesbetweenthem.Foragivenhomologousseries,theboilingpointsofthemembercompoundsrisefairlyregularlywithincreasingmolecularweight.在温度、Tp,那里的蒸汽压力达到101.3kPa。开始煮和xTp被称为正常沸点液体的x。在这个温度，当蒸汽压达到101.3kPa时，液体x开始沸腾，这个蒸汽压力被叫做x的正常沸点。任何一种液体在它的蒸汽压达到101.3kPa之前都不分解，每种液体的沸点都有
5、其自身的特点。一般来说,一种物质的沸点取决于它的分子质量和它们之间的引力的强度。对于一个给定的同系物，其成员化合物的沸点随分子量的增加而增加。Polarliquidstendtoboilhigherthannonpolarliquidsofthesamemolecularweight,andassociatedpolarliquidsusuallyboilconsiderablyhigherthannonassociatedpolarcompounds.极性液体的沸点往往高于相同分子量的非极性液体，而相关的极性液体的沸点远远高于一般的极性化合物。Theboilingpointisacharac
6、teristicconstantthatiswidelyusedintheidentificationofliquids.Becauseofitsmarkeddependenceuponpressureanditsrathererraticresponsetoimpurities,however,itisgenerallylessreliableandusefulincharacterizationandasacriterionofpuritythanisthemeltingpointforsolids1.沸点是一个常数,广泛用于识别液体。然而，由于对压力的显著依赖性和对杂质的相当无规律的反应
7、，沸点用于鉴别和作为纯度的判据方面，较之固体的熔点一般不太可信和较少使用。BoilingPointsofSolutions沸点的解决方案Thenormalboilingpointofanysolutionisthetemperatureatwhichthetotalvaporpressureofthesolutionisequalto101.3kPa.Theeffectofanysolute,Y,ontheboilingpointofXwilldepend,then,uponthenatureofY.IfYislessvolatilethanX.thenthetotalvaporpressur
8、eofthesolutionislower,atanygiventemperature,thanthevaporpressureofpureX.正常沸点的任何解决方案都是在其溶液总蒸汽压力等于101.3kPa时的温度。任何溶质，Y在X上的沸点的效果将取决于Y的性质。如果Y比X难挥发。那么其总蒸汽压都比在任何给定的温度下纯X的蒸汽压低。SuchacaseisrepresentedbycurveBC,inwhichtheexperimentallydeterminedvaluestorthevaporpressuresofasolutionareplottedagainsttemperature.
9、Thevaporpressureofthesolutiondoesnotreach101.3kPa.untilatemperatureTpisattained.Inotherwords,thepresenceofthelessvolatilesoluteraisestheboilingpointofXfromTptoTp.Asolutionofsugarorsaltinwaterisafamiliarexampleofthistypeofsolution.根据溶质所确定实验值来绘制温度-蒸汽压力图，如曲线BC所示。直到温度达到Tp时，其溶液的蒸汽压才达到101.3kPa。换句话说,较低挥发性溶
10、质的存在使X的沸点从Tp提高到Tp。这种类型的一个广为人知的例子就是糖或盐溶解在水中。Figure5.Generalizedvaporpressurediagramsforapureliquid(BO,forasolutioninwhichthesoluteislessvolatilethanthesolvent(BC),andforasolutioninwhichthesoluteismorevolatilethanthesolvent(BC).图5。广义水汽压图表示纯液体(BC,溶液中溶质比溶剂(BC)难挥发，以及另一溶液中含有更不稳定的溶剂(B“C”)。Ontheotherhand,if
11、YismorevolatilethanX.thenthetotalvaporpressureofthesolutionishigherthanthatofpureX,asshownbycurveBC.Thevaporpressureofsuchasolutionreaches101.3kPa.attempratureTp;hencetheeffectofthemorevolatilesoluteistolowertheboilingpointofXfromTptoTp.Asolutionofacetoneinwaterisanexampleofthistype.另一方面,如果Y比X更易挥发。那
12、么其溶液的总蒸汽压比纯X的高。,如图所示曲线BC所示。当一溶液的蒸汽压力达到101.3kPa、温度达到Tp,因此更多的挥发性溶质的作用是使X的沸点从TP降低到TP。丙酮在水中的溶液就是这种类型的一个例子。InanysolutionoftwoliquidsXandY,themoleculesofXaredilutedbymoleculesofY,and,conversely,themoleculesofYaredilutedbymoleculesofX.YouwouldthereforeexpectthevaporpressureduetoXtobelessthanthatofpureX;inf
13、act,youmightpredictthatthePARTIALPRESSUREduetoXwouldbeproportionaltothemolecularconcentrationofX.在任何溶液中的两种液体X和Y，X的分子被Y的分子稀释，相反,Y的分子被X的分子稀释。你因此会认为由此X的蒸汽压就小于纯的X。事实上,你可以预测,X的局部压力,与X的组分的浓度成正比。Similarly,thepartialpressureofYmightbeexpectedtobeproportionaltothemolecularconcentrationofY.Thisis,infact,therelationshipwhichholdsforso-calledidealsolutions.ItisexpressedinRaoultsLaw-thepartialpressureofacomponentinasolutionatagiventemperatureisequaltothevaporpressureofthepuresubsta
