EnergyandThermochemistry Lesson3.1
Introduction
Everythingwedoisconnectedinonewayoranotherwithenergy.Notonlyourmodernsocietybutlifeitselfdependsonenergyforitsexistence.Theissuessurroundingenergy–itssources,production,distribution,andconsumption–pervadeconversationsinscience,politics,andeconomics,andrelatetoenvironmentalconcernsandpublicpolicy.Think:Listonecurrenteventtopicsthatyoumightunderstandbetterifyouhadabetterunderstandingofenergy.WiththeexceptionofenergyfromtheSun,mostoftheenergyusedinourdailylivescomesfromchemicalreactions.Thecombustionofgasoline,theproductionofelectricityfromcoal,theheatingofhomesbynaturalgas,andtheuseofbatteriestopowerelectronicdevicesareallexamplesofhowchemistryisusedtoproduceenergy.Evensolarcellsrelyonchemistrytoproducethesiliconandothermaterialsthatconvertsolarenergydirectlytoelectricity.Inaddition,chemicalreactionsprovidetheenergythatsustainslivingsystems.Plantsusesolarenergytocarryoutphotosynthesis,allowingthemtogrow.Theplantsinturnprovidefoodfromwhichwehumansderivetheenergyneededtomove,maintainbodytemperature,andcarryoutallotherbodilyfunctions.Listthreewaysweuseenergyinourdailylives:Think:Itisevidentthatthetopicofenergyisintimatelyrelatedtochemistry.Whatexactlyisenergy,though,andwhatprinciplesareinvolvedinitsproduction,consumption,andtransformationfromoneformtoanother?Writedownyourthoughtsaboutthisquestionnow.Thermodynamicsdefinition:Energy:Work:Heat:
EnergyandThermochemistry Lesson3.1
Howcanenergybetransferredfromoneobjecttoanother:KineticEnergyPotentialEnergy
ElectrostaticPotentialEnergyandCoulomb’sLaw
EnergyandThermochemistry Lesson3.1
ConservationofEnergyUnitsofEnergySystemandSurroundings
Twowaystotransferenergy:WorkandHeatWork:Heat:
EnergyandThermochemistry Lesson3.1
FirstLawofThermodynamicsInternalEnergyRelatingΔEtoHeatandWorkSignconventionsSampleProblem:GasesA(g)andB(g)areconfinedinacylinderandpistonarrangementlikethatinFigure5.4andreacttoformasolidproductC(s):A(g)+B(g)èC(g).Asthereactionoccurs,thesystemloses1150Jofheattothesurroundings.Thepistonmovesdownwardasthegasesreacttoformasolid.Asthevolumeofthegasdecreasesundertheconstantpressureoftheatmosphere,thesurroundingsdo480Jofworkonthesystem.Whatisthechangeintheinternalenergyofthesystem?
EnergyandThermochemistry Lesson3.1
EndothermicandExothermicProcessesEndothermicExothermic
EnergyandThermochemistry Lesson3.1
StateFunctionsEnthalpydefinition:Pressure-VolumeWork
EnergyandThermochemistry Lesson3.1
SampleProblem:Afuelisburnedinacylinderwithapiston.Theinitialvolumeofthecylinderis0.250Landthefinalvolumeis0.980L.Ifthepistonexpandsagainstaconstantpressureof1.35atm,howmuchwork(inJ)isdone?(1L-atm=101.3J)
EnergyandThermochemistry Lesson3.1
EnthalpyChangeSampleProblemIndicatethesignoftheenthalpychange,ΔH,inthefollowingprocessescarriedoutunderatmosphericpressureandindicatewhethereachprocessisendothermicorexothermic.(a)Anicecubemelts;(b)1gofbutane(C4H10)iscombustedinsufficientoxygentogivecompletecombustiontoCO2andH2O.
