Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 26 CH101 A1 (MWF 9 am)
TP Theenthalpydiagramshowschangesassociatedwiththereaction
Na2 g Br2 g  2NaBr g .
Theuppermosthorizontallinecorrespondstothespecies…
25%
25%
25%
25%
Wednesday, November 9, 2016
•
•
•
•
2Na s Br2 l
2Na g 2Br g
Na2 g Br2 g
somethingelse
1.
2.
3.
4.
Hess’slaw
StandardstatesandstandardΔrH
Standardenthalpyofformation,ΔfH o
UsingΔfH o’stocomputeanyΔrH
Nextlecture: Calorimetry,pp231–232,doneinlab ;Bond
enthalpies,ΔbH ;UsingΔbH ’stoestimate ΔrH.
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Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
∆r
Ho
Copyright © 2016 Dan Dill [email protected]
via Hess’s law
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
∆r
Consider
Ho
via Hess’s law
Consider
A⟶ BΔrH o1
A⟶ BΔrH o1 85kJ
C⟶ BΔrH o2
C⟶ BΔrH o2 ‒52kJ
A⟶ CΔrH
o
3
A⟶ CΔrH o3 ?
?
Sinceenergyisconserved...
Δr H
Copyright © 2016 Dan Dill [email protected]
o
3
ΔrH
o
1
ΔrH
Sinceenergyisconserved...
o
ΔrH o3 ΔrH o1 ΔrH o2 85kJ– ‒52kJ 137kJ
2
Illustratewiththeenthalpydiagramfortheseprocesses.
7
Copyright © 2016 Dan Dill [email protected]
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1
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
∆rHo via Hess’s law
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
∆rHo via Hess’s law
Consider
Consider
C s O2 g ⟶ CO2 g ΔrH
1
C s O2 g ⟶ CO2 g ΔrH o1 393.5kJ
S s O2 g ⟶ SO2 g ΔrH o2
S s O2 g ⟶ SO2 g ΔrH o2 296.8kJ
CS2 l 3O2 g ⟶ CO2 g 2SO2 g ΔrH o3
CS2 l 3O2 g ⟶ CO2 g 2SO2 g ΔrH o3 1103.9kJ
C s 2S s ⟶ CS2 l ΔrH o4 ?
C s 2S s ⟶ CS2 l ΔrH o4 ?
o
Sinceenergyisconserved...
Δr H
o
4
ΔrH
o
1
Sinceenergyisconserved...
2ΔrH
o
2
ΔrH
o
ΔrH o4 ΔrH o1 2ΔrH o2 ΔrH o3 116.8kJ
3
9
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
∆r
Ho
Copyright © 2016 Dan Dill [email protected]
via Hess’s law
10
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Standard states and standard ∆rH
First,getexpressionforΔrH .
o
Then,substituteinvaluesintheexpressionforΔrH o togetitsnumericalvalue.
IngeneralΔrH dependsontheformofreactantsandproducts.
ForthisreasonwemustspecifytheseformswhentabulatingvaluesforΔrH .
Standardstatesaredefined,fortemperatureofinterest,for…
• puresubstancesasthemoststableform
• gasesasatpressure1bar
• aqueousspeciesasat1M
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Copyright © 2016 Dan Dill [email protected]
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Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Standard states at 25 oC (http://goo.gl/aljmi)
Bromine?
Br2 l
Standardenthalpyofformation,ΔfH o
Mercury?
Hg l
Sodiumsulfate?
Na2SO4 s
Ethanol?
CH3CH2OH l
Hydratedchlorideionsinaqueoussodiumchloridesolution?
1MCl aq
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Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Standard enthalpy of formation,
Copyright © 2016 Dan Dill [email protected]
∆fHo,
of X
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
∆fHo of
FormonemoleofX…
…fromtheelements itcontains,…
…eachintheirstandardstate.
Copyright © 2016 Dan Dill [email protected]
sugar, C6H12O6(s)
Formonemoleofsugar…
 C6H12O6 s
…fromtheelements itcontains,…
C,H,andO
…eachintheirstandardstate,
C s ,H2 g ,andO2 g
Recall,thestandardstateofanelementisitsmoststableform.
16
Copyright © 2016 Dan Dill [email protected]
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3
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
∆fHo of sugar, C6H12O6(s)
∆fHo of sugar, C6H12O6(s)
Thestandard enthalpyofformationofsugarisdefinedastheenthalpychange
whenonemole ofsugarisformedfromitselements,eachintheirstandard
states.
Task:Writedownthebalancedchemicalequationwhoseenthalpychangeis
thestandardenthalpyofformationofsugar,C6H12O6 s
Theenthalpychange,ΔrH, ofthechemicalreaction
6C s 6H2 g 3O2 g  C6H12O6 s
isthestandardenthalpyofformationofsugar,ΔfH˚.
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Lecture 26 CH101 A1 (MWF 9 am) Fall 2016
19
Copyright © 2016 Dan Dill [email protected]
TP Theenthalpydiagramshowschangesassociatedwiththereaction
Na2 g Br2 g  2NaBr g .
Theuppermosthorizontallinecorrespondstothespecies…
25%
25%
25%
25%
1.
2.
3.
4.
2Na s Br2 l
2Na g 2Br g
Na2 g Br2 g
somethingelse
23
Copyright © 2016 Dan Dill [email protected]
4