Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:16 PM
Copyright © 2016 Dan Dill [email protected]
TP Inacertainchemicalreaction,10kJofheatflowintothesystemandthe
systemdoes21kJofworkonthesurroundings.ThismeansΔU = …
13%
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31kJ
21kJ
11kJ
10kJ
‒10kJ
‒11kJ
‒21kJ
‒31kJ
Lecture 22 CH101 A1 (MWF 9 am)
Friday, October 28, 2016
Beginch7:Chemicalreactionsandenergyflows
• Firstlawofthermodynamics
• Systemvs.surroundings
• Detectingheatandwork
Nextlecture: Amountofheatdependsonwhetherthereiswork
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
First law of thermodynamics
Energy,U,isexchanged betweensystem andsurroundings asheat,q,and
work,w,
ΔU = q + w
Ch 7:ChemicalReactionsandEnergyFlows
Positive valuesincrease energyofsystem
ΔU q w
q heatflowintothesystem
w doneonthesystem
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Copyright © 2016 Dan Dill [email protected]
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:16 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
TP Inacertainchemicalreaction,10kJofheatflowintothesystemandthe
systemdoes21kJofworkonthesurroundings.ThismeansΔU = …
First law of thermodynamics
Inacertainchemicalreaction,10kJofheatflowintothesystemandthesystem
does21kJofworkonthesurroundings.Sketchtheenergydiagramshowingq,
w,andΔU forthisreaction.Indicatetheinitialandfinalenergybyhorizontal
lineslabeledUi andUj,respectively.
13%
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31kJ
21kJ
11kJ
10kJ
‒10kJ
‒11kJ
‒21kJ
‒31kJ
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Chemical system, chemical surroundings
Systemvs.surroundings
Ininchemicalreactions,energychangeisduetobondbreakingandbond
makingasreactantsbecomeproducts.
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Copyright © 2016 Dan Dill [email protected]
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:16 PM
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
TP Aqueoussolutionsatthesametemperaturearecombined,areaction
occurs,andthetemperatureofthecombinedsolutionsgoesup.Thewater is...
Chemical system, chemical surroundings
Ininchemicalreactions,energychangeisduetobondbreakingandbond
makingasreactantsbecomeproducts.
33% 1. thesystem
33% 2. thesurroundings
33% 3. neithersystemnorsurroundings
The“system”isthecollectionofreactantsandproducts.
The“surroundings”iseverythingelse.
Inaqueousreactions,thecontainingwaterispartofthesurroundings.
Heatreleasedbythe“system”warmsthesolution.
Heatabsorbedbythe“system”coolsthesolution.
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
TP Aqueoussolutionsatthesametemperaturearecombined,areaction
occurs,andthetemperatureofthecombinedsolutionsgoesup.Thereactants
are...
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Copyright © 2016 Dan Dill [email protected]
Reactants are only part of the system
Is
2A B⇌A A B B
thesystem
thesurroundings
partofthesystem
partofthesurroundings
endothermic q 0 orexothermic q 0 ?
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:16 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Reactants are only part of the system
Reactants are only part of the system
Is
Wecannottellwhether
2A B⇌A A B B
2A B⇌A A B B
endothermic q 0 orexothermic q 0 ?
Ingeneral,energychangesinchemicalreactionsareduetobothbondbreaking
andbondbreaking.
2A B⇌2A 2B
isendothermic q 0 orexothermic q 0 withoutknowingwhetherthe
energyneedforbondbreaking
2A B⇌2A 2B
islargerorsmallerthantheenergyreleaseofbondmaking
isendothermic,sincebreakingbondsalwaysrequiresenergy
2A⇌A Aand2B⇌B B
Thatis,toknowthesignofqwemustalwaysconsiderbothreactantsand
products,andforthisreason,inchemicalreactions,thesystemconsistsofboth
thereactantsandproducts.
2A⇌A Aand2B⇌B B
areeachexothermic,sincemakingbondsalwaysreleasesenergy
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Quiz Aceticaciddissolvesinwaterasaweakelectrolyte,
CH3COOH aq H2O l  H3O aq CH3COO aq
Intheaceticacidsolution,theacetateion,CH3COO aq ,is…
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Detectingheatandwork
thesystem
thesurroundings
partofthesystem
partofthesurroundings
Response
Counter
Copyright © 2016 Dan Dill [email protected]
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:16 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
How do we know heat is present?
How do we know heat is present?
Sinceqsurr mc ΔTsurr …
wecanusetemperaturechangeofsurroundingstomonitorheat flow.
Sinceqsurr mc ΔTsurr …
wecanusetemperaturechangeofsurroundingstomonitorheat flow.
Temperatureincrease insurroundings, ΔTsurr 0,means…
energyflowoutofsystemintosurroundings…
energyofsystemgoesdown…
andso,q 0.
Temperaturedecrease insurroundings, ΔTsurr 0means…
energyflowintosystemfromsurroundings…
energyofsystemgoesup…
andso,q 0.
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Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Lecture 22 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
TP WhenNaHCO3 s isdissolvedin200mLofHCl aq ,thetemperature of
thesolutiongoesdown.Thismeansthechemicalreactionbetweenthe
NaHCO3 s andtheHCl aq resultsinthechemicalsystem …
For chemical processes, Tsys does not change
ForA A⇌2A,energyisrequiredtobreakthebonds
EnergycomesfromsurroundingsandsoTsur goesdown
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Sincethisenergyisusedtobreakthebonds,Tsys doesnotchange
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Copyright © 2016 Dan Dill [email protected]
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givingoffheatandsoq
givingoffheatandsoq
absorbingheatandsoq
absorbingheatandsoq
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