Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
TP “InmylectureIwastoldthatchangeinenthalpyisproductsminus
reactants,butmydiscussionleadertoldmethatitisreactantsminusproducts.
I’vealsolookedinanotherchemistrybookanditsayproductsminusreactants.
Whichisright?”
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Lecture 27 CH101 A1 (MWF 9 am)
Friday, November 11, 2016
• UsingΔfH
o’stocomputeanyΔ
rH
Nextlecture: Bondenthalpies,ΔbH ;UsingΔbH ’stoestimate ΔrH ;If
somesubstancesarenotgases,usingΔbH ’sworkspoorly;Beginch 8:
ModelingatomsandtheirelectronsReview:Whatlightisandhowit
interactswithmatter;Naturalfrequenciesofatoms;Lightandmatter
exchangeenergysmoothlyandslowly
productsminusreactants
reactantsminusproducts
both
neither
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Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
2 H2(g) + O2(g)  2 H2O(g)
UsingΔfH o’stocomputeanyΔrH
Sketchtheenthalpydiagramforthisreaction,labellingthenenthalpychangeas
Δ1 H .
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Copyright © 2016 Dan Dill [email protected]
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Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
2 H2(g) + O2(g)  2 H2O(g)
2 H2(g) + O2(g)  2 H2O(g)
Add“2H2O l ”toyourdiagram.
Addanarrowtoyourenthalpydiagramfor2H2 g O2 g  2H2O l ,
andlabelthearrowΔ2H.
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Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
9
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
2 H2(g) + O2(g)  2 H2O(g)
TP Basedonyourdiagram,Δ3His…
Addanarrowtoyourenthalpydiagramfrom2H2O l to2H2O g ,
andlabelthearrowΔ3H.
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SinceΔ1H Δ2H Δ3H ,…
Δ3H Δ1H – Δ2H
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Copyright © 2016 Dan Dill [email protected]
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Copyright © 2016 Dan Dill [email protected]
ΔfH H2O,g
2ΔfH H2O,g
ΔvapH H2O
2ΔvapH H2O
–ΔvapH H2O
–2ΔvapH H2O
Somethingelse
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Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
2 H2(g) + O2(g)  2 H2O(g)
2 H2(g) + O2(g)  2 H2O(g)
UseyourdiagramtowritetheexpressionforΔvapH H2O interms
ofΔ1H andΔ2H.
UseyourdiagramtowritetheexpressionforΔvapH H2O interms
oftheenthalpiesofformationofliquidandgaseouswater.
ΔvapH H2O ½ Δ1H Δ2H ΔvapH H2O ΔfH H2O,g ΔfH H2O,l 12
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
2 H2(g) + O2(g)  2 H2O(g)
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Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Copyright © 2016 Dan Dill [email protected]
Using ∆fH˚’s to compute ∆rH
Theenthalpyofformationofgaseouswateris–241.8kJandthatofliquid
wateris–285.8kJ.EvaluateΔvapH H2O .
4NH3 g 5O2 g  4NO g 6H2O g
4NH3 g  2N2 g 6H2 g
5O2 g  5O2 g
2O2 g 2N2 g  4NO g
6H2 g 3O2 g  6H2O g
ΔvapH H2O …
ΔfH H2O,g ΔfH H2O,l –241.8kJ– –285.8kJ 44.0kJ
ΔH 1
ΔH 2
ΔH 3
ΔH 4
4ΔHf NH3,g
0
4ΔHf NO,g
6ΔHf H2O,g
Hess’slaw:ΔrH ΔH1 ΔH2 ΔH3 ΔH4
4ΔHf NO,g 6ΔHf H2O,g 4ΔHf NH3,g
Note:Elementsinstandardstatesareabsent
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Copyright © 2016 Dan Dill [email protected]
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Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
2/6/2017 1:15 PM
Copyright © 2016 Dan Dill [email protected]
Copyright © 2016 Dan Dill [email protected]
TP “InmylectureIwastoldthatchangeinenthalpyisproductsminus
reactants,butmydiscussionleadertoldmethatitisreactantsminusproducts.
I’vealsolookedinanotherchemistrybookanditsayproductsminusreactants.
Whichisright?”
Using ∆fH˚’s to compute any ∆rH
The keyfeatureofstandardenthalpiesofformation isthat,
theenthalpychangeofanyreaction,ΔrH,canbecomputedusingthem,
as…
ΔrH Sum ΔfH products – Sum ΔfH reactants
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Copyright © 2016 Dan Dill [email protected]
Lecture 27 CH101 A1 (MWF 9 am) Fall 2016
1.
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3.
4.
productsminusreactants
reactantsminusproducts
both
neither
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