freezing point depression - valencia college, orlando, florida：冰点抑郁症-瓦伦西亚学院，奥兰多，佛罗里达州

《freezing point depression - valencia college, orlando, florida：冰点抑郁症-瓦伦西亚学院，奥兰多，佛罗里达州》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、FreezingPointDepressionReneeY.BeckerValenciaCommunityCollegeIntroductionSolutionsthatcontainnonvolatilesoluteshaveahigherboilingpointandalowerfreezingpointthantheinitialpuresolvent.Thesecolligativepropertiesresultfromthefactthatthevaporpressureofasoluti

2、onwithanonvolatilesoluteislowerthanthevaporpressureofthepuresolvent.Rememberthatacolligativepropertyisaphysicalpropertyofasolutionthatdependsonthenumber,butnotthekind,ofsoluteparticlesinagivenamountofsolvent.Thevaporpressureofaliquidisdeterminedbytheabi

3、lityofparticlesattheliquidssurfacetoescapeintothevaporphase.Whenweaddasolutetoapuresolventsomeofthespacesatthesurfaceoftheliquidwillbeoccupiedbythenonvolatilesolute.Sincesomeofthespacesaretakenbythesolutefewersolventparticlesareinapositiontoescapeintoth

4、egasphase.Thismeansthatthesolutionsvaporpressureislowerthanthepuresolvent’svaporpressureatalltemperatures.Theboilingpointofasubstanceiswhenthevaporpressureisequaltotheatmosphericpressure.Sincethesolutedecreasesthevaporpressuremoreheatneedstobeaddedforth

5、evaporpressureofthesolutiontobeequaltotheatmosphericpressure.Thisiswhysolutionswithanonvolatilesolutehavehigherboilingpointsthanthepuresolvent.Vaporpressureloweringalsocausesfreezingpointdepression(seeFigure1).Thefreezingpointofasubstanceisthetemperatur

6、eatwhichitssolidandliquidphasescoexistinequilibrium.Thefreezingpointdepressionofasolutionisthedecreaseinthefreezingpointofasolventcausedbythepresenceofasolute.Anotherwaytostatethisisthatthefreezingpointofasolutionisthetemperatureatwhichthesolventinasolu

7、tionandthepuresolidsolventhavethesamevaporpressure.Vaporpressureloweringresultsinfreezingpointdepressionprovidedthatthesolutiondoesnotfreezeasasolidsolution.Thesolidthatformsmustbethepuresolvent.Figure1:VaporPressureDiagramforWaterandanAqueousSolutionWa

8、terSolutionLiquidSolventSolidSolventPressure,atmDtbDtfTemperature13FreezingPointDepressionWecanrelatethefreezingpointdepressionofapuresolvent,Dtf,tothemolalityofthesolution(m),asseeninEquation1and2.(1)Dtf=tsolvent–tsolution(2)Dtf