AP Chemistry Spring 2020 Mr. Cameron€¦ · reaction o =n p ΔG f ∑o(products)−n r ΔG f...
Transcript of AP Chemistry Spring 2020 Mr. Cameron€¦ · reaction o =n p ΔG f ∑o(products)−n r ΔG f...
APChemistrySpring2020Mr.Cameron
1stLawofThermodynamics
Spontaneous?
• Considerthefollowingphysicalandchemicalprocesses– Awaterfallrunsdownhill,butneveruphill,spontaneously
– Alumpofsugarspontaneouslydissolvesinacupofcoffee,butsugardoesnotspontaneouslyreappearinitsoriginalform
– Waterfreezesspontaneouslybelow0˚C,andicemeltsspontaneouslyabove0˚C(at1atm).
Spontaneous?
• Considerthefollowingphysicalandchemicalprocesses– HeatflowsfromahoIerobjecttoacolderone,butthereverseneverhappensspontaneously.
– Theexpansionofagasinanevacuatedbulbisaspontaneousprocess.Thegatheringofallthemoleculesintoonebulbisnotspontaneous.
Spontaneous?
• Considerthefollowingphysicalandchemicalprocesses– Apieceofsodiummetalreactsviolentlywithwatertoformsodiumhydroxideandhydrogengas.However,hydrogengasdoesnotreactwithsodiumhydroxidetoforwaterandsodium.
– Ironexposedtowaterandoxygenformsrust,butrustdoesnotspontaneouslychangebacktoiron.
Spontaneous
• AreacNonthatdoesoccurunderthegivensetofcondiNonsiscalledspontaneous.
• ProcessesthatoccurspontaneouslyinonedirecNoncannot,underthesamecondi:on,alsotakeplacespontaneouslyintheoppositedirecNon.
• Spontaneousdoesnotmeanfast.Itdoesmeanthatitiscertaintooccur.
Entropy-S
• Adirectmeasureofrandomnessordisorderofasystem.
• Adrivingforceforaspontaneousprocessisanincreaseintheentropyoftheuniverse.
Entropy-S
• Entropyiscloselyrelatedtoprobability• ThemorewaysaparNcularstatecanbeachieved,thegreateristhelikelihoodoffindingthatstate.
• NaturespontaneouslyproceedstowardthestatesthathavethehighestprobabiliNesofexisNng.
PosiNonalEntropy
Processesthatleadtoanincreaseinentropy(ΔS>0)
2ndLawofThermodynamics
• Inanyspontaneousprocessthereisalwaysanincreaseintheentropyoftheuniverse.
• Theentropyoftheuniverseincreasesinaspontaneousprocessandremainsunchangedinanequilibriumprocess.
ASpontaneousProcess:ΔSuniv = ΔSsys +ΔSsurr >0AEquilibriumProcess:ΔSuniv = ΔSsys +ΔSsurr =0
EffectsofTemperature
• LookingatΔSsysandΔSsurr,consider:
• WhatisthesignofΔSsys
• WhatisthesignofΔSsurr
H2O(l)⎯→⎯ H2O(g)
EffectsofTemperature-CharacterisNcs
• SignofΔSsurr:dependsonthedirecNonoftheflowofheat– Exothermicprocessesincreasetheentropyofthesurroundings
– Endothermicprocessesdecreasetheentropyofthesurroundings
EffectsofTemperature-CharacterisNcs
• MagnitudeofΔSsurr:dependsonthetemperature
• “Howmuchwillthetransferofheataffectthesurroundings?”– DependsdirectlyonthequanNtyofheattransferred
– Dependsinverselyonthetemperature
CalculaNngΔSsurr
• Constanttemperature:K• Constantpressure• NegaNvesignbecauseΔHisdeterminedwithrespecttothesystem.
ΔSsurr = −
ΔHT
PracNceCalculaNngΔSsurr
InthemetallurgyofanNmony,thepuremetalisrecoveredviadifferentreacNons,dependingonthecomposiNonoftheore.Forexample,ironisusedtorecoveranNmonyinsulfideoresandcarbonisusedforoxideores.CalculateΔSsurrforeachofthesereacNonsat25˚Cand1atm.
Sb2S3(s)+3Fe(s)⎯→⎯ 2Sb(s)+3FeS(s)ΔH = −125kJSb4O6(s)+6C(s)⎯→⎯ 4Sb(s)+6CO(g)ΔH =778kJ
GibbsFreeEnergy(FreeEnergy)
• IfΔG>0–NotSpontaneous
• IfΔG=0–SystematEquilibrium
• IfΔG<0–SpontaneousJosiahWillardGibb
ΔG = ΔH −TΔS
FreeEnergy–Spontaneous?Case SignofΔHsys SignofΔSsys SignofΔG Spontaneous?1 - +2 + -3 - -4 + +
3rdLawofThermodynamicsTheentropyofapurecrystallinesubstanceatabsolute
zeroisS=0at0K.
CalculaNngΔHo,ΔSoandΔGo
ΔHreactiono = npΔHf
o(products)−∑ nrΔHfo(reactants)∑
ΔSreactiono = npΔS
o(products)−∑ nrΔSo(reactants)∑
ΔGo = ΔHo −TΔSo
PracNceCalculaNngΔHo,ΔSoandΔGo
ConsiderthereacNon
carriedoutat25˚Cand1atm.CalculateΔHo,ΔSo,andΔGo.
2SO2(g)+O2(g)⎯→⎯ 2SO3(g)
CoupleofThoughtsonΔGo
• StateFuncNon–CanuseHess’sLaw• CanuseΔGo
f:
ΔGreactiono = npΔGf
o(products)−∑ nrΔGfo(reactants)∑
APChemistrySpring2020Mr.Cameron