This one talks about energy, and Chemistry

Talks about chemistry

1. ENERGY AND CHEMISTRY
Chemistry for Engineers
Melody B. Morata, RChE

2. Windfarmslikethe
oneshownhereare
one ofseveral
alternativeenergy
technologiesthathave
growninimportancein
recentyears.Despite
theseadvances,fossil
fuelswillcontinueto
providethebulkofour
energyforthe
foreseeablefuture.
Kevan O'Meara,
2009/Shutterstock.com

3. Introduction
Ifyoulistapplicationsofchemistrythatareimportantinyour
life,manyofthemwouldbelikelytoinvolveenergyand
energytransformation.Welookedattheburningoffuelsas
anapplicationofchemicalcombustion.

4. Introduction
Allthebatteriesyoudependontopowerportableelectrical
devicesarebasedonchemicalreactionsaswell.Inthis
chapter,wewilltakeacloserlookatenergyanditsrolein
chemistry.

5. Defining Energy
Most people have an intuitive feel for the concept of energy, and we
see the word every day. Breakfast cereals advertise their ability to
provide energy in the morning. In sports, substitute players are
described as boosting their team’s energy.

6. Defining Energy
The energy crisis brought on by oil embargoes in the 1970s is a critical
component of the history of that decade, and energy remains central to
important political issues in the 21st century.

7. Defining Energy
This widespread use of the concept of energy underscores its
importance. It also suggests that we’ll need to be very careful in
defining energy and related terms because it is apparent that in casual
use the word “energy” conveys many related but subtly different
meanings.

8. Forms of Energy
Most of the energy we encounter can be placed into two broad
categories: potentialenergy and kineticenergy.

9. Forms of Energy
Potentialenergyisassociatedwith
therelativepositionofanobject.
Forexample,arollercoastergains
potentialenergyasitispulledupthe
initialslopebecauseitacquiresa
higherpositionrelativetotheground
andgravityisattractingitdownward.

10. Forms of Energy
Butgravityisnottheonlyforceresponsibleforobjectshavingpotential
energy.Theattractionandrepulsionbetweenelectricalchargesalso
leadtopotentialenergy.

11. Forms of Energy
Kineticenergyisassociatedwith
motion.
Whentherollercoasterheadsdown
thefirsthill,ittransformspotential
energyintokinetic
energy.

12. Forms of Energy

13. Forms of Energy
Therollercoasterexampleshowskineticandpotentialenergyona
macroscopicscale.Butonamicroscopiclevel,allsubstancesandobjects,
fromfuelstothepaperhavethesesameformsofenergy.Anysubstance
orobjectiscomposedofatomsandmolecules.

14. Forms of Energy
Atomsandmoleculeshavekineticenergyassociatedwiththeirconstant
motion,andtheyhavepotentialenergyduetothevariousforcesthey
exertononeanother.Thecombinedkineticandpotentialenergiesofthe
atomsandmoleculesthatmakeupanobjectconstituteitsinternal
energy.

15. Forms of Energy
Thustherollercoastercarshavethreebasicformsofenergy:kinetic
(fromtheirmotion),potential(fromtheirpositionrelativetotheground),
andinternal(fromthemoleculesthatcomposethematerialsfromwhich
theyaremade).

16. Forms of Energy
Muchoftheinternalenergyofanobject,beitarollercoastercarora
pieceofcoal,isassociatedwiththepotentialenergyarisingfromthe
relativepositionsoftheatomsthatmakeuptheobject.

17. Forms of Energy
Themakingorbreakingofchemical
bondschangesthispotentialenergy.
Inmostchemicalreactions,bondsare
brokeninthereactantsandnewbonds
areformedintheproducts.Ifthe
amountofenergyliberatedinbond
makingisgreaterthanthatconsumed
inbondbreaking,theoverallprocess
releasesenergy.

18. Forms of Energy
Thisenergyreleaseisoftenreferredtoaschemicalenergy,andthe
harnessingofchemicalenergyisanimportantaspectoftheoverlap
betweenchemistryandengineering.

19. Example Problem
1.Howfast(inmeterspersecond)mustanironballwithamassof56.6
gbetravelinginordertohaveakineticenergyof15.75J?
2.Whatisthekineticenergyofasinglemoleculeofoxygenifitis
travelingat1.5×10
3
m/s?

20. Example Problem
3.Thekineticenergyofmoleculesisoftenusedtoinducechemical
reactions.ThebondenergyinanO
2moleculeis8.22×10
–19
J.CananO
2
moleculetravelingat780m/sprovideenoughenergytobreaktheO"O
bond?WhatistheminimumvelocityofanO
2moleculethatwouldgivea
kineticenergycapableofbreakingthebondifitisconvertedwith100%
efficiency?

21. Heat and Work
Althoughwecanuseawidevarietyofclassificationsfortypesofenergy,
allenergyflowiseitherheatorwork.We’llneedtounderstandboth
formsofenergytransfertoassesstheenergyeconomyoftheworldand
theroleofchemistryinthateconomy.

22. Heat and Work
Heatistheflowofenergybetweentwoobjects,fromthewarmeroneto
thecoolerone,becauseofadifferenceintheirtemperatures.Thusifwe
arespeakingcarefully,heatisaprocessandnotaquantity.

23. Heat and Work
Althoughweroutinelyhearstatementssuchas“turnuptheheat,”heatis
notanentitywecanpumpintoaroomoracupofcoffee.
Anobjectdoesnotpossessheat.Inastrictlyscientificsense,afurnace
doesnotproduceheatbutratherabodyofwarmairorhotwaterthathas
ahighertemperaturethanthecoolairinaroom.
Whatemergesfromtheventonthefloorisnot“heat,”butwarmair.
Althoughthesedistinctionsareessentiallysemantic,theycanbevery
importantinmanycases.

24. Work
Workisthesecondformofenergytransfer.Workisthetransferofenergy
accomplishedbyaforcemovingamasssomedistanceagainstresistance.

25. Work
Whenweconsidermacroscopicexamples,wearetypicallyviewingwork
intermsofmechanicalenergy.Work,however,encompassesawider
rangeofphenomenathanjustmechanicalmovementofmacroscopic
objects.

26. Work
Themostcommontypeofworkwewillencounterinchemicalprocesses
ispressure-volumework(PV-work).

27. Work
Whenagasexpands,itcandowork.

28. Work
Foramoreproductiveexampleofworkbeingdonebyachemical
reaction,wemightlookattheburningofgasolineinacarengine.
https://youtu.be/ZQvfHyfgBtA

29. Work
Theenergyneededtopropelacarisreleasedbythecombustionofthose
hydrocarbonsintheenginecylinders.
Thiscombustionproducescarbondioxideandwatervapor,andthose
gasesdoPV-workastheyexpandagainstthepistoninthecylinder.This
PV-workisthentransmittedthroughthedrivetraintomovethecar.

30. Energy Units
TheSIunitofenergyisthejoule(J),and1jouleisequalto1kgm
2
/s
2
.
Realizingthatworkshouldhaveunitsofenergyhelpsustomakesenseof
thisunit.Workisforcetimesdistance,andforceismasstimes
acceleration.Thus,workis

31. Energy Units
Ifwethinkaboutchemistryonamolecularlevelbreakingasingle
chemicalbondtypicallyrequiresonlyabout10
–18
J.Considerbreakinga
moleofbonds.Inthatcase,breakingonemoleofC-Hbonds,forexample,
requiresabout410kJ.

32. Energy Units
Manyolderunitsforenergyreliedonsomereadilyobservableproperty
fortheiroriginaldefinition:
•theBtu,wasfirstdefinedastheamountofenergyneededtoraisethe
temperatureof1lbofwaterby1°F.
•traditionalunitforenergyisthecalorie,whichwasoriginallydefinedas
theamountofenergyrequiredtoheat1gofwaterfrom14.5to15.5°C.

33. Energy Units
•Acalorieisdefinedas4.184J
•ABtuisdefinedas1055J
•TheCaloriereportedforfoodsisactuallyakilocalorie.(ThefoodCalorie
shouldbewrittenwithanuppercase“C.”)Thus,1Calorieisactually
equivalentto4184J,or4.184kJ.

34. Energy Transformation and Conservation of
Energy
Inmanycasesitisdesirabletotransformenergyfromoneforminto
another.Forexample,thelightinginyourroomisprovidedbyelectricity,
butthatelectricitywasgeneratedbythereleaseofchemicalenergy
throughthecombustionofcoal.

35. Energy Transformation and Conservation of
Energy
Unlessyouwanttotrytolightyourroombyburningachunkofcoal,you
needawaytoharnessthechemicalenergyreleasedasthecoalburnsand
thenconvertittoelectricalenergy.Thatelectricalenergymustthenbe
conveyedtoyourroom,whereyourlightbulbsconvertitintoradiant
energy.

36. Energy Transformation and Conservation of
Energy
Nowwebegintoconsiderthelawsofnaturethatapplywhenoneformof
energyisconvertedintoanother.Thelawofconservationofenergystates
thatenergycanneitherbecreatednordestroyed-onlyconvertedfrom
oneformofenergytoanother.

37. Energy Transformation and Conservation of
Energy
Ifweaccountproperlyforallenergyconversionandenergytransfer
processes,thetotalamountofenergypresentmustremainconstant.To
accountproperlyforalltypesofenergy,wewillneedtodefineanumber
oftermsquitecarefully.

38. Energy Transformation and Conservation of
Energy
First,wemustspecifypreciselywhatisbeingstudied.Thesystemis
definedasthepartoftheuniversethatisbeingconsidered.The
remainderoftheuniverseisreferredtoasthesurroundings.

39. Energy Transformation and Conservation of
Energy
Thesedefinitionsassurethatthesystemplusthesurroundingsmustequal
theuniverse.Thesystemandthesurroundingsareseparatedbya
boundary.

40. Energy Transformation and Conservation of
Energy
Onceanappropriatechoiceofasystemhasbeenmade,theconceptof
conservationofenergyimmediatelybecomesuseful.

41. Energy Transformation and Conservation of
Energy
Becausewesaidthatheatandworkaretheonlypossibleformsofenergy
transfer,wecanattributetheoverallchangeinenergy,E,ofasystemto
thesetwocomponents.Heatiscommonlydesignatedasqandworkasw,
sowecanwrite

42. Energy Transformation and Conservation of
Energy
Thesymbol∆(delta)isintroducedhereasanotationmeaning“the
changein.”Thissymbol,whichwillbeusedfrequentlyin
thermodynamics,isalwaysdefinedasthedifferencebetweenthefinal
stateandtheinitialstate.

43. Energy Transformation and Conservation of
Energy
Theequationbelowisdeceptivelysimplebecauseitincludesarbitrary
choicesforthemeaningofthesignsforthequantitiesofheatandwork.
Again,thekeyistochooseconsistentdefinitionsforthosesigns.

44. Energy Transformation and Conservation of
Energy
Conventiondictatesthatenergytransferredintoasystemisgivena
positivesignandenergyflowingoutofasystemcarriesanegativesign.

45. Energy Transformation and Conservation of
Energy
Thuswhenheatflowsintoasystemfromthesurroundings,thevalueofq
ispositive,andwhenworkisdoneonasystem,thevalueofwispositive.
Conversely,whenheatflowsoutofasystemorworkisdonebythe
systemonthesurroundings,qandwwillbenegative.

46. Example Problem
1.If515Jofheatisaddedtoagasthatdoes218Jofworkasaresult,
whatisthechangeintheenergyofthesystem?
2.Ifamachinedoes4.8×10
3
kJofworkafteraninputof7.31×10
4
kJof
heat,whatisthechangeininternalenergyforthemachine?
3.Whichsystemdoesmorework:(a)∆E=–436J,q=400J;or(b)∆E=
317J,q=347J?

47. Heat Capacity and Calorimetry
Laboratoryrequiresasystematicwaytomeasureenergyflow.Wecando
thisbyobservingheatflowintooroutofasystemthroughasetof
techniquescollectivelycalledcalorimetry.

48. Heat Capacity and Calorimetry
Theidentityofthesubstanceisincludedthroughatermcalledthespecific
heatcapacity(c,usuallysimplycalledthespecificheat),leadingto
equation
Thespecificheatisaphysicalpropertyofamaterialthatmeasureshow
muchheatisrequiredtoraisethetemperatureofonegramofthat
materialby1°C.

49. Heat Capacity and Calorimetry
Similarly,themolarheatcapacityisaphysicalpropertythatdescribeshow
muchheatisrequiredtoraisethetemperatureofonemoleofa
substanceby1°C.
Soifwechoosetoexpresstheamountofmaterialintermsofmoles
ratherthanmass,ourequationchangesonlyslightly.ThesubscriptponC
p
indicatesthatthisistheheatcapacityatconstantpressure.

50. Heat Capacity and Calorimetry

51. Example Problem
1.Themolarheatcapacityofliquidwateris75.3J/molK.If37.5gof
wateriscooledfrom42.0to7.0°C,whatisqforthewater?
2.Copperwiresusedtotransportelectricalcurrentheatupbecauseof
theresistanceinthewire.Ifa140-gwiregains280Jofheat,whatis
thechangeintemperatureinthewire?Copperhasaspecificheatof
0.384J/g°C.

52. Example Problem
3.Apieceoftitaniummetalwithamassof20.8gisheatedinboiling
waterto99.5°Candthendroppedintoacoffeecupcalorimetercontaining
75.0gofwaterat21.7°C.Whenthermalequilibriumisreached,thefinal
temperatureis24.3°C.Calculatethespecificheatcapacityoftitanium.
Waterhasaspecificheatof4.184J/g°C.