Le Châteliers Principle
Le Châtelier's Principle. “If a chemical system at equilibrium experiences a change in concentration temperature
Chemical Equilibria and Le Châteliers Principle—CH142L
Chemical Equilibria and Le Châtelier's Principle—CH142L. February 11 2014. Maine Line Heating
Le Chateliers Principle – NO2/N2O4 tubes
Description: Le Chatelier's principle is demonstrated by invoking a color change inside a sealed tube containing NO2 (brown) and N2O4 (colorless) gases at.
Green Chemistry - Equilibrium/Le Chateliers Principle
Educational Goals: • Provide students with an understanding of the concept of chemical equilibrium and to demonstrate. Le Chatelier's Principle i.e. if a
Le Chateliers Principle
Le Chatelier-Braun principle states that various secondary processes induced by the fluctuation also tend to restore a homogeneous state of the system.
Global Strong Le Chatelier-Samuelson Principle
In this paper the Le Chatelier principle for a Leontief model due to Samuelson and. Morishima is extended to a more general system of nonlinear equations.
A quantitative approach to Le Chateliers principle
11-Feb-2009 A quantitative approach to Le Chatelier's principle ... you have used extensively in a qualitative manner: the principle of Le Chatelier.
The Le Chatelier Principle as a Corollary to a Generalized Envelope
Le Chatelier principle asserts that as constraints are added to the first- order equilibrium conditions then where the subscript outside the parentheses
EXCEPTIONS TO THE LE CHATELIER PRINCIPLE
account of Le Chatelier's principle.) Consider for example
©2 7www.beyondbenign.org Equilibrium/LeChatelier'sPrincipleModifiedfromanactivityoriginallycreatedbyparticipatingteachers.2008SummerGreenChemistryWorkshop.TeacherBackgroundInformation:Traditionally,equilibriumexperimentsandLeChatelier'sPrincipleareillustratedusingthefollowingexperiments.Inthisexperiment,everyday,non-toxicmaterialsreplacethesematerials.exo(A)CoCl42-+6H2O!Co(H2O)62++4Cl-blueendoredThisexperimentisusedtodemonstratetheeffectsofbothtemperaturechangesandconcentrationchangesonanequilibriummixture.(B)Cr2O72-+H2O!2CrO42-+2H+orangeyellowThisexperimentisusedtodemonstratetheeffectsofconcentrationchangesonanequilibriummixture.(C)Fe3++CNS-!Fe(CNS)2+yellowredThisexperimentisalsousedtodemonstratetheeffectsofconcentrationchangesonanequilibriummixture.SafetyInformation:Safetyglassesshouldbeusedwheneverworkinginthelab.Iodineisaminoreyeirritantandvinegarandammoniacancauseskinirritation.EducationalGoals:• ProvidestudentswithanunderstandingoftheconceptofchemicalequilibriumandtodemonstrateLeChatelier'sPrinciple,i.e.ifastressisappliedtoasystematequilibrium,thesystemreadjuststorelievethestressapplied.StudentObjectives:Studentswill...• Explaintheconceptofchemicalequilibrium• Distinguishbetweenstaticanddynamicequilibrium• StateLeChatelier'sPrinciple• Describehowtosetupanexperimentthatisatchemicalequilibrium• PredicttheeffectofaddingastresstothesystematequilibriumHIGHSCHOOLGreenChemistry
©2 7www.beyondbenign.org Time:45minutesMaterials(pergroupof2-4students):• Bottleofsodawater• Balloon• Matches• Candle• Universalindicator• 5Erlenmeyerflasks• Blacktea• Vinegar• Ammonia-cleaningsolution• Tinctureofiodine• Starchspray• Drinkingstraw• Hotplate• Icebath• Glassstirringrods• TesttubeTeacherPrep:• Starchsolution:Spraystarchintoa4 mLbeaker(coverthebottomofthebeakerwithsprayoruse5- dropsofliquidstarch).Filltheremainderofthebeakerwithwaterandstir.• Blacktea:Preparea mLbeakerofblackteathedarkerthebetter.Preparewithelectrickettleandallowittocooltoroomtemperature.TeacherDemonstrationActivator(Optional):Materials:• Bottleofsodawater• balloon• Candle• Matches• UniversalindicatorProcedure:CarryouttheTeacherDemonstrationanddiscussinclassasanintroductiontoLeChatelier'sPrincipleandtheconceptofequilibrium.• Introducetoclasstheideaofabottleofsodawater.Doesequilibriumexistinsidethebottle?• Whatgasispresentinthebottle(dissolvedandabovethesolution)?• Removegasfrombottlebyshakingandthentrappingthegasintheballoon.• Testforgasbypouringsomeofgasoveralightedcandle.Whatcanwededuce?• Bubblegasintolitmusindicatororcabbagejuice(orbetter,limewater).Thegasisacidic(orturnslimewatermilky)-whatisthenameoftheacidinthesodawater?• Discusstheequilibriuminsidethebottle:CO2+H2O!H2CO3Activity1-IodineandStarch• Assignpre-labforhomeworkandreviewequilibrium• Introducetheconceptofthestarch-iodinecomplex.Isthisanexampleofanequilibriumreaction?• Addaonedropoftinctureofiodineto3 mlofstarchsolution.Notetheformationofablue-blackcolor.• Heatthesolutiontoabout8 °C.Notethattheblue-blackcolordisappears.Whatcanwededucefromthis?
©2 7www.beyondbenign.org • Coolthecontainerbyplacingitinice.Whatdoweobserve?• Discussequilibriumwiththeclass:Iodine+Starch!Starch-IodineComplexcolorlessblue-blackThesolublestarchactsasan"indicator"ofmoleculariodine.TheshiftsinequilibriumpositionproducedbytemperaturechangesareinaccordancewithLeChatelier'sprinciple.ΔHis+ve(endothermic)intheforwarddirectionaswrittenabove.Warmingthesolutioncausesa'shift'totherightandthesolutionbecomesblue(andviceversabecauseΔHforthereactionis-ve,exothermic,inthereversedirection).Whenitschilledmorestarchiodinecomplexisformedwhichcreatesthedarkercolor.Whenheatisaddedasastressorthestarchiodinecomplexiscolorless.Whichdirectionisexothermicandwhichisendothermic?Howdoweexplainourresults?exoIodine+Starch!Starch-Iodinecomplexcolorlessendoblue-blackActivity2-Tea• Eachstudentgroupwillprepare6 mlblackteasolutionfromastocksolutionpreparedbytheteacher.• Studentswillthenseparate2 mlintothreetesttubesorsmallErlenmeyerflasks.Oneofthesewillbeusedasacontrol.• Tooneofthesamples,adda 5dropsofvinegar.Notethechangeincolortoalightercolorcomparedtothecontrol.ThisindicatestheincreaseinthenumberofH+ions.Thenumberofdropsofvinegarcanbemanipulated.Whathappenswhenyouaddlessormore?• Toanotherflask,add5dropsofammoniacleaningsolution.Notethechangetoadarkercolorcomparedtothecontrol.ThebasicsolutionofammoniaremovestheH+ions.Againthenumberordropscanbechanged-askstudentstotry3trialsandrecordthevariables.• Studentscanthenusetheflashlightfeatureontheircellphonestoseethechanges.• Discussshiftingoftheequilibrium:Tea+H+!TeaH+darklightcolorKeysforSuccess:• Introducethelessoncoveringthefollowingpoints:• Youmayhavecomeacrosstheword"equilibrium"inyourstudyofphysics• Ifyoulookupthemeaningof"equilibrium"inadictionaryyouwillfinditexplainedusingwordslike"stateofbalance".Ameterstickwhichissuspendedatitscenterofgravityissaidtobebalancedorinequilibrium.Ametersticksuspendedatitscenterofgravityremainsstationaryorstatic.Thus,thistypeofequilibriumisoftenreferredtoasstaticequilibrium.Inotherwords,theentiresystemisnotmoving.• Considernowthecaseofamanrunningonatreadmill.Overall,thereisnochangeinthepositionoftheman.Heisrunningforwardatthesamespeedasthebeltismovingintheoppositedirection.Thetwoopposingmotionsbalanceeachother.Thisisanexampleofatypeofequilibriumcalleddynamicequilibrium,theworddynamicmeans"moving".• Anotherexampleofadynamicequilibriumisifyouwalkdownanescalatoratthesamespeedasitis
©2 7www.beyondbenign.org movingup.Thereisnooverallchangeinyourpositionbecausethetwoopposingmotionsarebalanced.• Chemicalequilibriumisastateofdynamicbalancewheretherateoftheforwardreactionisthesameastherateofthebackwardreaction.• ExamplesofreactionsatequilibriumN2+3H22NH32NO2(g)N2O4(g)DisposalInformation:• Allwastesafefordisposaldownthedrain
©2 7www.beyondbenign.org LeChatelier'sPrinciplePreLabExerciseBackgroundInformation:Chemicalequilibriumisastateofdynamicbalancewheretherateoftheforwardreactionisthesameastherateofthebackwardreaction.Examplesofreactionsatequilibriumare:N2+3H2!2NH32NO2(g)!N2O4(g)Youmayhavecomeacrosstheword"equilibrium"inyourstudyofphysics.Ifyoulookup"equilibrium,"youwillfinditexplainedusingwordslike"stateofbalance."Ameterstickwhichissuspendedatitscenterofgravityissaidtobebalancedorinequilibrium.Ametersticksuspendedatitscenterofgravityremainsstationaryorstatic.Thus,thistypeofequilibriumisoftenreferredtoasstaticequilibrium.Inotherwords,theentiresystemisnotmoving.Considernowthecaseofamanrunningonatreadmill.Overall,thereisnochangeinthepositionoftheman.Heisrunningforwardatthesamespeedthatthebeltismovingintheoppositedirection.Thetwoopposingmotionsbalanceeachother.Thisisanexampleofatypeofequilibriumcalleddynamicequilibrium,theworddynamicmeans"moving."Anotherexampleofadynamicequilibriumisifyouwalkdownanescalatoratthesamespeedasitismovingup.Thereisnooverallchangeinyourpositionbecausethetwoopposingmotionsarebalanced.Problem:HowcanLeChatelier'sPrinciplebeusedtopredictthedirectioninwhichasystematequilibriumwillshiftwhenconditionsarealtered?TheequilibriumsystemthatwewillstudyinthePre-Labis:CuCl2(aq)!Cu+2(aq)+2Cl- (aq)+heatgreenbluecolorless . WriteoutthebalancedreactionbetweenAgNO3(aq)andCuCl2(aq)andidentifytheprecipitateformed.2. Foreachchangelisted,predicttheequilibriumshift,usingthereactionfromquestionnumberoneandyourknowledgeofLeChatelier'sPrinciple:StressDirectionofShift(!;";ornochange)RaisetemperatureLowertemperatureAddAg+NO3-AddNa+Cl-
©2 7www.beyondbenign.org LeChatelier'sPrincipleStudentSheetActivity1-IodineandStarchMaterials:• Starchsolution• mLgraduatedcylinder• 3xtesttubes( 8x 5 mm)• Tinctureofiodine• Plasticpipettes• Glassstirringrod• Ice• 2x3 mLbeakers• Thermometer• Hotplate/electrickettle• TesttuberackProcedure: . Measure6 mLofstarchsolutionusingagraduatedcylinder.2. Pour2 mLofthestarchsolutionintothreeseparatetesttubes.3. Add dropoftinctureofiodinewiththeplasticpipettetoeachtesttubeandstirwithaglassstirringrod.4. Prepareanicebathwithicecubesandwaterina3 mLbeaker.5. Prepareahotwaterbathbyheatinga3 mLbeakerfilledwithwateronahotplateuntilitreaches8 C;measurethetemperaturewithathermometer.(Alternatively,heatwaterinanelectrickettleandthentransfertoa3 mLbeaker(fastermethod).6. Placeonetesttubeintheicebath,oneinthehotwaterbath,andleaveoneasacontrol(notstressed).7. Observeandrecordthechangesthatoccur.Activity2-TeaMaterials:• Blackteasolution• mLgraduatedcylinder• 3x( 8x 5 mm)testtubes• 2xplasticpipettes• Vinegar• Ammoniacleaningsolution• GlassstirringrodProcedure: . Measure75mLofblackteasolutionwithgraduatedcylinder.2. Pourtheteaintothreetesttubesthereshouldbe25mLofteaineach.3. Useaplasticpipettetoadd 5dropsofvinegartooneofthebeakers,stirwithastirringrod,andlabel.4. Useadifferentpipettetoadd5dropsofhouseholdammoniatothesecondbeaker,stirwithastirringrod,andlabel.5. Leavethethirdbeakerasacontrol.6. Observeandrecordthecolorchangesthatoccur.
©2 7www.beyondbenign.orgLeChatelier'sPrincipleName:_________________________________________Activity1-IodineandStarchDataandObservations:Iodine+Starch!Starch-IodineComplexcolorlessblue-blackStressResultingColorControlRaisetemperatureLowertemperatureQuestions: . Whateffectdidheatingthetesttubehaveontheconcentrationofstarch-iodinecomplex?ExplainhowyouknowthisbyusingLeChatelier'sPrinciple.2. Whateffectdidcoolingthetesttubehaveontheconcentrationofstarch-iodinecomplex?ExplainhowyouknowthisbyusingLeChatelier'sPrinciple.3. Whichdirectionisexothermic?Whichdirectionisendothermic?Explainyourresults.
©2 7www.beyondbenign.orgActivity2-TeaDataandObservations:Tea+H+!TeaH+darklightcolorStressResultingColorControlVinegaradditionAmmoniaadditionQuestions: . Inthisactivity,howcouldyoudeterminewhetherornotachangeoccurredinequilibrium?Explain.2. ForeachreactioninActivity2,demonstratehoweachchangecanbeexplainedbyLeChatelier'sPrinciple.Bespecificaboutwherethechemicalwasadded(thestress)anditsimpactontheothercomponentsoftheTeaEquilibrium.Vinegar(Aceticacid,HC2H3O2):Tea+H+#TeaH+darklightcolorAmmonia(NH3):Tea+H+#TeaH+darklightcolor3. DidtheseactivitieshelpyoutounderstandLeChatelier'sPrinciple?Whyorwhynot?4. Explainwhythisisagreenchemistrylab.
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