chapter 5 thermochemistry - michigan state university · chapter 5 thermochemistry the energy of...
TRANSCRIPT
![Page 1: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/1.jpg)
Chapter 5 Thermochemistry
The energy of chemical reactions How do you keep track of it? Where does it come from?
![Page 2: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/2.jpg)
Energy
• Theabilityto:• dowork• transferheat.
Ø Work:Energyusedtocauseanobjectthathasmasstomove.
Ø Heat:Energyusedtocausethetemperatureofanobjecttorise.
![Page 3: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/3.jpg)
Units of Energy
• TheSIunitofenergyisthejoule(J).• Anolder,non-SIunitissHllinwidespreaduse:Thecalorie(cal). 1cal=4.184J
Energyhasunitsof(mass)(velocity)2RememberkineHcenergywas1/2mv2
1 J = 1 ⎯⎯ kg m2
s2
![Page 4: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/4.jpg)
Work • Energyusedtomoveanobjectoversomedistance.
• w=F� d,w=work,F=forced=distanceoverwhichtheforceisexerted.
Noteunits:F=ma,mass(distance/s2)W=F(d)=mass(distance2/s2)=mv2
![Page 5: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/5.jpg)
Heat
• Energycanalsobetransferredasheat.
• Heatflowsfromwarmerobjectstocoolerobjects.
![Page 6: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/6.jpg)
Kinetic Energy
EnergyanobjectpossessesbyvirtueofitsmoHon.
1 2
KE = ⎯ mv2
![Page 7: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/7.jpg)
PotenHalEnergy
EnergyanobjectpossessesbyvirtueofitsposiHonorchemicalcomposiHon.
More potential E
Less P.E. as bike goes down.
![Page 8: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/8.jpg)
TransferalofEnergy
a) AddP.E.toaballbyliUingittothetopofthewall
![Page 9: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/9.jpg)
TransferalofEnergy
a) AddP.E.toaballbyliUingittothetopofthewall
b) Astheballfalls,P.E------>K.E.(1/2mv2)
![Page 10: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/10.jpg)
TransferalofEnergy
a) AddP.E.toaballbyliUingittothetopofthewall
b) Astheballfalls,P.E------>K.E.(1/2mv2)Ballhitsground,K.E.=0,butEhastogo
somewhere.So1. Ballgetssquashed2. Heatcomesout.
![Page 11: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/11.jpg)
Energy accounting
• WemustidenHfywheredifferenttypesofenergygo.
• Therefore,wemustidenHfytheplaces.
![Page 12: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/12.jpg)
System and Surroundings
• Thesystemincludesthemoleculeswewanttostudy(here,thehydrogenandoxygenmolecules).
• Thesurroundingsareeverythingelse(here,thecylinderandpiston).
![Page 13: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/13.jpg)
First Law of Thermodynamics • Energyisconserved.• Inotherwords,thetotalenergyoftheuniverseisaconstant;ΔESystem=-ΛEsurroundings
![Page 14: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/14.jpg)
InternalEnergyTheinternalenergyofasystemisthesumofallkineHcandpotenHalenergiesofallcomponentsofthesystem;wecallitE.
Einternal,total= EKE + EPE + Eelectrons + Enuclei +…… Almost impossible to calculate total internal energy Instead we always look at the change in energy (ΔE).
![Page 15: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/15.jpg)
InternalEnergyBydefiniHon,thechangeininternalenergy,ΔE,isthefinalenergyofthesystemminustheiniHalenergyofthesystem: ΔE=Efinal−EiniHal
![Page 16: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/16.jpg)
ChangesinInternalEnergy
• IfΔE>0,Efinal>EiniHalØ Therefore,thesystemabsorbedenergyfromthesurroundings.
Ø Thisenergychangeiscalledendergonic.
![Page 17: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/17.jpg)
ChangesinInternalEnergy
• IfΔE<0,Efinal<EiniHalØ Therefore,thesystemreleasedenergytothesurroundings.
Ø Thisenergychangeiscalledexergonic.
![Page 18: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/18.jpg)
ChangesinInternalEnergy
• Whenenergyisexchangedbetweenthesystemandthesurroundings,itisexchangedaseitherheat(q)orwork(w).
• Thatis,ΔE=q+w.
![Page 19: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/19.jpg)
ΔE,q,w,andTheirSigns
+q -q
hot plate adds heat to water
Surroundings suck heat out of water.
![Page 20: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/20.jpg)
Signofwork
Truck pushes block up. Does work on block wtruck- wblock+
block pushes truck down does work on truck wblock- wtruck+
![Page 21: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/21.jpg)
Exchange of Heat between System and Surroundings
• Whenheatisabsorbedbythesystemfromthesurroundings,theprocessisendothermic.
![Page 22: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/22.jpg)
Exchange of Heat between System and Surroundings
• Heatabsorbedbysystemfromsurroundings,isendothermic.
• Heatreleasedbysystemtosurroundings,theisexothermic.
![Page 23: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/23.jpg)
State Functions
Totalinternalenergyofasystem:K.E.+Eelectrons+Enucleus+P.E.totalvirtuallyimpossibletomeasure/calculate
![Page 24: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/24.jpg)
StateFuncHons• However,wedoknowthattheinternalenergyofasystemisindependentofthepathbywhichthesystemachievedthatstate.Ø Inthesystembelow,thewatercouldhavereachedroomtemperaturefromeitherdirecHon.
![Page 25: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/25.jpg)
StateFuncHons• Therefore,internalenergyisastatefuncHon.• becauseit’sPATHINDEPENDENT• Andso,ΔEdependsonlyonEiniHalandEfinal.
![Page 26: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/26.jpg)
StateFuncHons
• However,qandwarenotstatefuncHons.
• Whetherthebaceryisshortedoutorisdischargedbyrunningthefan,itsΔEisthesame.Ø Butqandwaredifferentinthetwocases.
![Page 27: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/27.jpg)
Work
processinanopencontainer(chemicalreacHoninabeaker)w?(cantherebeanywork)?Yes, evolving gases could push on the surroundings.
![Page 28: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/28.jpg)
Catch the work, do the same process in a cylinder
Process evolves gas, pushes on piston, work done on piston
![Page 29: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/29.jpg)
Catch the work, do the same process in a cylinder
w = F*d, F = P*A, d=Δh
w = -P*AΔh= -PΔV
Negative because an increase in Volume means that the system is doing work on the surroundings.
ΔE=q+w=q-PΔV qP = ΔE + PΔV
![Page 30: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/30.jpg)
Example• Gasinsidecylinderwith
electricheater.• Add100jheatwith
heater.• 1.Pistoncangoupand
down• 2.Pistonstuck.• a.WhathappenstoTin
eachcase?• b.Whataboutqandw
foreachcase?• c.WhataboutΔEineach
case?
![Page 31: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/31.jpg)
Example• Gasinsidecyclinderwithelectricheater.• Add100jheatwithheater.• 1.Pistoncangoupanddown• 2.Pistonstuck.• a.WhathappenstoTineachcase?• b.Whataboutqandwforeachcase?• c.WhataboutΔEineachcase? a.1. Piston goes up, some E
goes to expand gas, do work. T goes up less
a.2 T goes up more, all E goes to q.
b.1. both q and w positive
b.2. w 0, q larger c. ΔE the same & + in each case
![Page 32: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/32.jpg)
WorkNowwecanmeasurethework: w=−PΔV
Zn + 2HCl ---------> H2(g) + ZnCl2
![Page 33: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/33.jpg)
Work
Zn+2HCl--------->H2(g)+ZnCl2ImoleofZnreacts.Howmuchworkisdone(P=1atm,
densityofH2=0.0823g/L)?1moleofH2isproduced.
![Page 34: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/34.jpg)
Work
ImoleofZnreacts.Howmuchworkisdone(P=1atm,densityofH2=
0.0823g/L)?1moleofH2isproduced.Zn+2HCl--------->H2(g)+ZnCl21mol 1mol2.014g/mol2.014gd=m/VV=m/dV=2.014g/0.0823g/L=24.47LW=-PΔV=1atm(24.47L)=-24.47L(atm)
![Page 35: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/35.jpg)
Enthalpy(H)
H = E + PV
This is the definition of Enthalpy for any process Buy why do we care?
![Page 36: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/36.jpg)
Enthalpy
• atconstantpressure,ΔH,is(Δ = change in thermodynamics) ΔH=Δ(E+PV)
• Thiscanbewricen(ifPconstant) ΔH=ΔE+PΔV
H = E + PV
![Page 37: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/37.jpg)
Enthalpy
• SinceΔE=q+wandw=−PΔV(Pconst.)subsHtutetheseintotheenthalpyexpression: ΔH=ΔE+PΔV ΔH=(q+w)−w ΔH=q
• Note:trueatconstantpressure• qisastatefuncHonatconstP&onlyPVwork.
![Page 38: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/38.jpg)
H=E+PV• Because:• Ifpressureisconstant(likeopentoatmosphere,i.e.mostthings)and
w=ΔPV.heatflow(q)=H(enthalpy)ofsystem.And:HisastatefuncHon,soqisalso.butonlyintherightcondi6ons
![Page 39: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/39.jpg)
Endothermicvs.Exothermic
• AprocessisendothermicwhenΔHisposiHve.
![Page 40: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/40.jpg)
EndothermicityandExothermicity
• AprocessisendothermicwhenΔHisposiHve.
• AprocessisexothermicwhenΔHisnegaHve.
![Page 41: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/41.jpg)
Enthalpies of Reaction
Thechangeinenthalpy,ΔH,istheenthalpyoftheproductsminustheenthalpyofthereactants:
ΔH=Hproducts−Hreactants
![Page 42: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/42.jpg)
EnthalpiesofReacHonThisquanHty,ΔH,iscalledtheenthalpyofreacHon,ortheheatofreacHon.
![Page 43: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/43.jpg)
Reaction Enthalpy summary
1. Enthalpyisanextensiveproperty.2. ΔHforareacHonintheforwarddirecHon
isequalinsize,butoppositeinsign,toΔHforthereversereacHon.
3. ΔHforareacHondependsonthestateoftheproductsandthestateofthereactants.
![Page 44: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/44.jpg)
Enthalpy of reaction example
ConsiderthereacHon:2KClO3------->2KCl+3O2ΔH=-89.4kJ/mola.WhatistheenthalpychangeforformaHonof0.855molesofO2?
![Page 45: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/45.jpg)
EnthalpyofreacHonexampleConsiderthereacHon:2KClO3------->2KCl+3O2ΔH=-89.4kJ/mola.WhatistheenthalpychangeforformaHonof0.855molesofO2?
2KClO3 -------> 2KCl + 3O2 ΔH = -89.4 kJ/mol 0.855 mol ΔH = -89.4 kJ/3 mol O2(.855 mol O2) = -25.5 kJ
![Page 46: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/46.jpg)
Calorimetry
Sincewecannotknowtheexactenthalpyofthereactantsandproducts,
wemeasureΔHthroughcalorimetry,themeasurementofheatflow.
![Page 47: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/47.jpg)
HeatCapacityandSpecificHeat
• heatcapacity:amountofErequiredtoraisethetemperatureofsomethingby1K
• specificheat:amountofErequiredtoraisethetemperatureof1gofasubstanceby1K.
![Page 48: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/48.jpg)
Heat Capacity and Specific Heat
Specificheatis:
Specific heat = heat transferred
mass × temperature change
s = q
m ΔT
smΔT = q
![Page 49: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/49.jpg)
Constant Pressure Calorimetry
indirectlymeasuretheheatchangeforthesystembymeasuringtheheatchangeforthewaterinthecalorimeter.
![Page 50: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/50.jpg)
Constant Pressure Calorimetry
Becausethespecificheatforwateriswellknown(4.184J/g-K),wecanmeasureΔHforthereacHonwiththisequaHon:q=m×s×ΔT
m=masss=specificheat
![Page 51: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/51.jpg)
ExampleWhena3.88gsampleofsolid
ammoniumnitratedisolvesin60.0gofwaterinacoffeecupcalorimeter,thetemperaturedropsfrom23.0°Cto18.4°C.(a)CalculateΔH(inkJ/molammoniumnitrate)forthesoluHonprocess.Assumethatthespecificheatisconstantand=1.0cal/gC.(b)Isthisprocessendothermicorexothermic?
![Page 52: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/52.jpg)
ExampleWhena3.88gsampleofsolidammoniumnitratedisolvesin60.0gofwaterina
coffeecupcalorimeter,thetemperaturedropsfrom23.0°Cto18.4°C.(a)CalculateΔH(inkJ/molammoniumnitrate)forthesoluHonprocess.Assumethatthespecificheatisconstantand=4.184J/g°C.(b)Isthisprocessendothermicorexothermic?
Reaction: NH4NO3(s) ------> NH4
+(aq) + NO3-(aq)
gr 3.88 g MW 80.04 g/mol #Mol 3.88 g/80.04 g/mol = 0.0484 mol Mass of solution = 3.88 g + 60 g = 63.88 g.
System: Solid AmNO3 Surroundings: Solution
q = s(specific heat)m(mass)ΔT q = s(J/g°C)m(grams)(Tfinal - Tinitial) qsolution = 4.184(J/g°C)(63.88 g)(18.4°C - 23.0°C) = -1229 J qwater=-qammonium nitrate = +1229 J ΔH(per mol NH4NO3) = 1.229 kJ/.0484 mol = 25.39 kJ/mol (b) Endothermic
![Page 53: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/53.jpg)
Bomb Calorimetry
ReacHonscanbecarriedoutseparatedfromthewaterina“bomb,”suchasthisone,
AndsHllmeasuretheheatabsorbedbythewater.
![Page 54: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/54.jpg)
Bomb Calorimetry
• Becausethevolumeinthebombcalorimeterisconstant,whatismeasuredisreallytheΔE,notΔH.
• FormostreacHons,• ΔE≈ΔH• Why?
![Page 55: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/55.jpg)
BombCalorimetry
H = E + PV ΔH = ΔE + ΔPV In a bomb calorimeter, ΔV = 0 For a process that doesn’t evolve gas: ΔP ≈ 0 as well. ΔH = ΔE + ΔPV = ΔE
![Page 56: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/56.jpg)
Example • A50gsampleofgasolinewasburnedbycombusHon
(withexcessoxygen)inacalorimeterwithaheatcapacityof10kJ/°C.Thetemperatureincreasedby100°C.CalculatethechangeinEpergofgasoline.
• qsurroundings=CΔΤ =10kJ/°C(100°C)=1000kJ
• qsurroundings=-qsystem• qsystem=-1000• -1000kJ/50g=-20kJ/g
• DoesΔΕ =ΔΗ inthiscase?
![Page 57: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/57.jpg)
Example • A50gsampleofgasolinewasburnedbycombusHon
(withexcessoxygen)inacalorimeterwithaheatcapacityof10kJ/°C.Thetemperatureincreased100°C.CalculatethechangeinEpergofgasoline.
• qsurroundings=CΔΤ =10kJ/°C(100°C)=1000kJ
• qsurroundings=-qsystem• qsystem=-1000• -1000kJ/50g=-20kJ/g
• DoesΔΕ =ΔΗ inthiscase?• NO!Pressurecan’tstayconstantinthiscase.
![Page 58: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/58.jpg)
Hess’s Law
• ΔHisknownformanyreacHons.• measuringΔHcanbeapain• CanweesHmateΔHusingΔHvaluesforotherreacHons?
![Page 59: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/59.jpg)
Hess’sLaw
Hess’slaw:statesthat:
ΔHfortheoverallreacHonwillbeequaltothesumoftheenthalpychangesfortheindividualsteps.
Yes!
![Page 60: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/60.jpg)
Hess’s Law
Why? BecauseΔHisastatefuncHon,
andispathwayindependent.OnlydependsoniniHalstateof
thereactantsandthefinalstateoftheproducts.
![Page 61: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/61.jpg)
Hess’slaw,example:• Given:• N2(g)+O2(g)---->2NO(g) ΔH= 180.7kJ• 2NO(g)+O2(g)---->2NO2(g)ΔH=-113.1kJ• 2N2O(g)---->2N2(g)+O2(g)ΔH= -163.2kJ• useHess’slawtocalculateΔHforthereacHon:• N2O(g)+NO2(g)---->3NO(g)
![Page 62: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/62.jpg)
Hess’slaw,example:• Given:• N2(g)+O2(g)---->2NO(g)ΔH= 180.7kJ• 2NO(g)+O2(g)---->2NO2(g) ΔH= -113.1kJ• 2N2O(g)---->2N2(g)+O2(g) ΔH= -163.2kJ• useHess’slawtocalculateΔHforthereacHon:• N2O(g)+NO2(g)---->3NO(g)
• N2O(g) ----> N2(g) + 1/2O2(g) ΔH = -163.2/2 =-81.6kJ • NO2(g) ----> NO(g) + 1/2O2(g) ΔH = 113.1 kJ/2=56.6kJ • N2(g) + O2(g) ----> 2NO(g) ΔH = 180.7
• N2O(g)+NO2(g)---->3NO(g) ΔH = 155.7 kJ
![Page 63: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/63.jpg)
EnthalpiesofFormaHonAnenthalpyofformaHon,ΔHf,isdefinedastheΔHforthereacHoninwhichacompoundismadefromitsconsHtuentelementsintheirmoststableelementalforms.
• 2Al + Fe2O3 -------> Al2O3 + 2Fe
• What is the heat of reaction given: • 2Fe + 3/2O2 -----> Fe2O3 ΔH = -825.5 KJ (heat of formation) • 2Al + 3/2O2 -----> Al2O3 ΔH = -1675.7 KJ (heat of formation)
![Page 64: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/64.jpg)
CalculaHonofΔH
• Imaginethisasoccurringin3steps:
C3H8 (g) + 5 O2 (g) ⎯→ 3 CO2 (g) + 4 H2O (l)
C3H8 (g) ⎯→ 3 C(graphite) + 4 H2 (g)
3 C(graphite) + 3 O2 (g) ⎯→ 3 CO2 (g) 4 H2 (g) + 2 O2 (g) ⎯→ 4 H2O (l)
![Page 65: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/65.jpg)
CalculaHonofΔH
• Imaginethisasoccurringin3steps:
C3H8 (g) + 5 O2 (g) ⎯→ 3 CO2 (g) + 4 H2O (l)
C3H8 (g) ⎯→ 3 C(graphite) + 4 H2 (g)
3 C(graphite) + 3 O2 (g) ⎯→ 3 CO2 (g) 4 H2 (g) + 2 O2 (g) ⎯→ 4 H2O (l)
![Page 66: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/66.jpg)
CalculaHonofΔH
• Imaginethisasoccurringin3steps:
C3H8 (g) + 5 O2 (g) ⎯→ 3 CO2 (g) + 4 H2O (l)
C3H8 (g) ⎯→ 3 C(graphite) + 4 H2 (g)
3 C(graphite) + 3 O2 (g) ⎯→ 3 CO2 (g) 4 H2 (g) + 2 O2 (g) ⎯→ 4 H2O (l)
![Page 67: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/67.jpg)
C3H8 (g) + 5 O2 (g) ⎯→ 3 CO2 (g) + 4 H2O (l)
C3H8 (g) ⎯→ 3 C(graphite) + 4 H2 (g)
3 C(graphite) + 3 O2 (g) ⎯→ 3 CO2 (g) 4 H2 (g) + 2 O2 (g) ⎯→ 4 H2O (l)
C3H8 (g) + 5 O2 (g) ⎯→ 3 CO2 (g) + 4 H2O (l)
CalculaHonofΔH
• ThesumoftheseequaHonsis:
Make each reactant or product from its elements This is called the heat of formation of a compound
![Page 68: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/68.jpg)
CalculaHonofΔH
WecanuseHess’slawinthisway:
ΔH=Σ n ΔHf(products)-Σ m ΔHf(reactants)wherenandmarethestoichiometriccoefficients.
° °
![Page 69: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/69.jpg)
StandardEnthalpiesofFormaHon
StandardenthalpiesofformaHon,ΔHf,aremeasuredunderstandardcondiHons(25°Cand1.00atmpressure).
°
![Page 70: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/70.jpg)
CalculaHonofΔH• CalculateΔHusingthetable:• C3H8(g)+5O2(g)----->3CO2(g)+4H2O(l)
![Page 71: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/71.jpg)
CalculaHonofΔH• C3H8+5O2----->3CO2+4H2OΔH = [3(ΔHfCO2) + 4(ΔHfH2O)] - [(ΔHf C3H8) + (5ΔHf O2)]
= [3(-393.5 kJ) + 4(-285.8 kJ)] - [(-103.85 kJ) + 5(0)
= [-1180.5 kJ + (-1143.2 kJ)] - [(-103.85 kJ)+ 0 kJ
= [-2323.7 kJ] - [-103.85 kJ)
= -2219.9 kJ
![Page 72: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/72.jpg)
Phase Changes • Conversionfromonestateofmacertoanotherisaphasechange.
• Energyiseitheraddedorreleasedinaphasechange.
• .
![Page 73: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/73.jpg)
Why is E (Q,H) transferred in phase change? • Atoms/molecules
sHcktoeachotherinliquid/solid,alwayssHckmoreinsolid.
• Atoms/moleculesdon’ttouchingas.
• Liquidtogas,Eisneededtopulltheatoms/moleculesfromeachother.
![Page 74: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/74.jpg)
Heating Curves
• AplotofTvs.q• Withinaphase:• q=ms• Thetemperatureofthesubstancedoesnotriseduringaphasechange.
• For the phase changes, the product of mass and the heat of fusion of vaporization is heat.
![Page 75: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/75.jpg)
Heating Curves
• AplotofTvs.q• Withinaphase:• q=ms• Thetemperatureofthesubstancedoesnotriseduringaphasechange.
• For the phase changes, the product of mass and the heat of fusion of vaporization is heat.
![Page 76: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/76.jpg)
Heating Curves
• AplotofTvs.q• Withinaphase:• q=msΔT• DuringmelHng:• q=ΔHFusm• Duringboiling:• q=ΔHvapm
• For the phase changes, the product of mass and the heat of fusion of vaporization is heat.
![Page 77: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/77.jpg)
Example:
• For the phase changes, the product of mass and the heat of fusion of vaporization is heat.
• Calculateqfortaking10gicefromAtoF:
![Page 78: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/78.jpg)
Example:
ΔHFus water: 334 J/g Δhvap water: 2444 J/g s water: 4.184 J/g°K s ice: 2.05 J/gK s vapor: 2.00 J/gK
![Page 79: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/79.jpg)
Example:
• Calculateqfortaking10gicefromAtoF:• A->B:(10g)2.05J/gK(25°C)=512.5J• B->C:10g(334J/g)=3340J• C->D:10g(4.184J/gK)(100K)=4184J• D->E:10g(2444J/g)=24440J• E->F:10g(2.00J/gK)(25K)=500J• TOTAL =32977J
ΔHFus water: 334 J/g Δhvap water: 2444 J/g s water: 4.184 J/g°K s ice: 2.05 J/gK s vapor: 2.00 J/gK
![Page 80: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/80.jpg)
EnergyinFoodsMostofthefuelinthefoodweeatcomesfromcarbohydratesandfats.
![Page 81: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/81.jpg)
What’sthedealwithfat?• Carbohydrates:• CnH2nOn+nO2-->-->-->nCO2+nH2O+Energy
• Fats:• CnH2nO2+mO2-->-->-->-->-->-->nCO2+nH2O
Fat storage.
more steps
It also clogs your arteries.
![Page 82: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/82.jpg)
Energy and oxidation states
• OxidaHonstateofCinafacyacid:
• OxidaHonstateofCinglucose:
• C6H8O6
CO2-
H3C
CO2-
HH
HH
HH
HH
HHHH
HHHH
![Page 83: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/83.jpg)
Energy and oxidation states
• OxidaHonstateofCinafacyacid:
• OxidaHonstateofCinglucose:
• C6H12O6
• O
• BothgotoCO2C:+4
CO2-
H3C
CO2-
HH
HH
HH
HH
HHHH
HHHH
-3 -2 -2 -2 -2 -2 -2 -2 +3
![Page 84: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/84.jpg)
FuelsThevastmajorityoftheenergyconsumedinthiscountrycomesfromfossilfuels.
![Page 85: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/85.jpg)
Majorissues• Portablefuel(liquid,relaHvelylight),transportaHon• Non-portablefuel(makeselectricity).
transportation
![Page 86: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/86.jpg)
TheEnergycycle:• Us(andalmosteverythingelsealiveontheearth):• C6H12O6+6O2---->6CO2+6H2O
• FossilfuelproducHon:• CH4+2O2---->CO2+2H2O(formethane)
• Plants:• 6CO2+6H2O+light---->C6H12O6+6O2
Net CO2 production could therefore be 0.
![Page 87: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/87.jpg)
Energy research on Campus ADREC
Anaerobic digestor
![Page 88: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/88.jpg)
Energy research on Campus ADREC
Anaerobic digestor • AnaerobicDigesHon:
• C6H12O6---->3CO2+3CH4
Basically:Poop---àCO2+CH4
bacteria
https://www.egr.msu.edu/bae/adrec/feature/south-campus-anaerobic-digester
![Page 89: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/89.jpg)
Hydrogen,theperfectfuel?2H2 + O2 -----> 2H2O ΔH = -285 kJ/mol H2(1mol/2g)= -142 kJ/g
This is literally what fuel cells do. You get nothing but water!
![Page 90: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/90.jpg)
Theproblemwithoil
• Not“renewable”(willrunout)• PolluHon(combusHonnotperfect).• Globalwarming
CO2absorbsheat.CnH2n+2+(3n+1/2)O2----->nCO2+(n+1)H2O
![Page 91: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/91.jpg)
![Page 92: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/92.jpg)
Efficiency/conservaHon
• U.S.coulddecreaseenergyneedsby20-50%bybeinglesswasteful.
• Highmileagecars• moreenergyefficientbuilding/homes.
![Page 93: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/93.jpg)
Hybridcar
• Gasenginepluselectricmotor• Why?• AlltheenergyissHllcomingfromburninggasoline.
![Page 94: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/94.jpg)
Hybrids• Electricmotorsareway
moreefficientthangasengines.(94%)
• Note,yourengineisveryhot,
• Itmustbecooled• FlushallthatEdowndrain.
Nowork,onlyheat.gas engines are 24-30% efficient
Problem: batteries suck! Heavy, expensive, limited recharging cycles, limited current etc.
![Page 95: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/95.jpg)
Liionbacery
x e- +xLi+ + Li1-xCo(IV)O2 -----> LiCo(III)O2
LixC6 ------> xLi+ + xe- + C6
Lithium is really light. Dissolves in organic solvents which are also light. Li is at the top of the activity series. Means a higher potential (more voltage per battery cell)
![Page 96: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/96.jpg)
Hybrids• Electricmotorsworkatlowspeeds• gasengineshutsoffwhennotneeded• atlowspeeds,stoplights,etc.• (infinitetorque,reallygofrom0-15)• Gasenginechargesbaceryandisusedathigherspeeds
• HybridsgetBETTERgasmilageintownversushighway
![Page 97: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/97.jpg)
OthersourcesHowmuchbangforyourbuck?
![Page 98: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/98.jpg)
TheproblemwithHydrogenStorage
gas, less dense, hard to get enough in the car and have trunk space
Kaboom (Hindenburg)
Where do you get the hydrogen?
![Page 99: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/99.jpg)
TheproblemwithHydrogenWhere do you get the hydrogen? (petroleum)
CH4(g) + H2O(g) ---à CO(g) + H2(g)
CO(g) +H2O(g) -à CO2(g) + H2(g)
![Page 100: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/100.jpg)
Ethanol,wheredoesitcomefrom
• AlcoholicfermentaHon:• C6H12O6---->2CO2+2C2H5OH(ethanol)ΔH=-76 kJ/mol • -1270 2(-393) 2(-280) • (anaerobic, bacteria & yeast can do this, we can’t)
Exactly the same place it comes from in your beer.
![Page 101: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/101.jpg)
Ethanol• AlcoholicfermentaHon:• C6H12O6---->2CO2+2C2H6O(ethanol)ΔH=-76 kJ/mol • -1270 2(-393) 2(-280) • (anaerobic, yeast can do this, we can’t) only to 10%. • Distillation (requires energy) to purify.
bug
Alcohol combustion: C2H6O + O2 ---> 2CO2 + 3H2O ΔH = -1367 kJ/mol(1mol/46g)=-29.7kJ/g
But why would this be better for global warming?
![Page 102: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/102.jpg)
Ethanol,problems• Lotsoflandtogrow(yield2-4tons/acre)• AllpresentagriculturallandinU.S.wouldnotbeenoughforall
transportaHonneeds.• requiresferHlizer,tractors,etc.forgrowing(energy)• DisHllaHonrequiresenergy• Forevery1.4kJneed1.0kJ,muchmorethanoil• Brazil,however,isapproaching50%ethanolfortransportaHon• Why?Sugarcane,largeststarchorsugaryield/acre.• But,youcan’tgrowsugarcaneonthegreatplains.
![Page 103: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/103.jpg)
Ethanol
• However,presentlyweonlyuseStarch,
O
H
HO
H
HO
H
OHH
HO
O
H
O
H
HOH
OH
H
H
OH
O
H
O
H
HOH
HO
OH
H
H
OH
O
H
HO
H
HO
H
H
OHH
OH
O
H
O
H
HO
H
H
OHH
OH
O
H
O
H
HO
H
H
OHH
OH
OH
not cellulose Most stuff in plants is cellulose
Two major types of carbohydrates in plants
![Page 104: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/104.jpg)
Cellulosicethanol
• 10+tons/acre(asopposedto2-4tons/acre)• Canuseanycrop,notjustfoodcropswithhighstarch(“switchgrass”).
• Problem:Breakingitdowntosmallsugarsthatyeastcanferment.
• Needcellulase,theenzymethatbreaksthisup.• ThisisacomparaHvelyeasyproblemtosolve• (comparedtohydrogen.)
Ethanol can work.
![Page 105: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/105.jpg)
Thingstoconsider
• Energyyield(howmuchEoutversusEin)?• Breakevenprice(howmuch/gallonofgasequivalents(presentcornethanolis2.25/gallonjusttomake).
• WhereisthetechnologyNOW?• Isstoragerequired,&ifso,howyougonnadoit• (solarwhenthesundoesn’tshine)• Remember,atpresentBaceriessuck!
![Page 106: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/106.jpg)
TheChemistryNobelPrize
• DanielShechtman,• Technion,Israel• For:• Thediscoveryof“quasi-crystals”in1984
![Page 107: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/107.jpg)
![Page 108: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/108.jpg)
TheChemistryNobelPrize• AnHo-Mg-Znquasi-crystal
Note, the five-fold symmetry of the faces! This was thought to be impossible! Is this a solid?
![Page 109: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/109.jpg)
TheThermitereacHon
• 2Al+Fe2O3------->Al2O3+2Fe
• WhatkindofreacHonisthis?• Whydoesithappen?• Usedforweldingrailroadtracks• WhatistheheatofreacHongiven:
• 2Fe+3/2O2----->Fe2O3ΔH=-825.5KJ• 2Al+3/2O2----->Al2O3 ΔH=-1675.7KJ
![Page 110: Chapter 5 Thermochemistry - Michigan State University · Chapter 5 Thermochemistry The energy of chemical reactions ... in the calorimeter. Constant Pressure Calorimetry Because the](https://reader031.vdocument.in/reader031/viewer/2022021821/5af787357f8b9a744490dfc4/html5/thumbnails/110.jpg)
TheThermiteReacHon • 2Al+Fe2O3------->Al2O3+2Fe
• WhatistheheatofreacHongiven:• 2Fe+3/2O2----->Fe2O3ΔH=-825.5KJ• 2Al+3/2O2----->Al2O3 ΔH=-1675.7KJ
• 2Al+3/2O2----->Al2O3 ΔH=-1675.7KJ• Fe2O3----->2Fe+3/2O2ΔH=825.5KJ
• 2Al+Fe2O3------->Al2O3+2FeΔH=-850.2KJ
http://www.youtube.com/watch?v=BnHR4cMXiyM
A thermite mystery: