Enthalpy of Reaction
Alfred Nobel
Chemistry Essentials - 053
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Enthalpy of Reaction
Reactants
Products
Bond Energies
- Bond Energies
Endothermic
!
Hess’s Law
Exothermic
!
!
Thermal Energy
Surroundings
Thermal Energy
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Thermite
Exothermic reaction
Energy Diagram
Energy
Reactants
y
p
l
a
Enth
ΔH
n
o
i
t
c
a
e
r
of
Products
Fe2O3 + 2Al
2Fe + Al2O3
Reaction Progress
ΔH = H(products) - H(reactants)
ΔH = -850kJ/mol
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Fe2O3 + 2Al
Thermite
Enthalpy Diagram
Reactants
Enthalpy
Enthalpy
ΔH= -850 kJ/mol
Fe2O3 + 2Al
2Fe + Al2O3
Products
2Fe + Al2O3
Enthalpy
ΔH = H(products) - H(reactants)
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Enthalpy Diagram
2Fe + Al2O3
Products
Enthalpy
Enthalpy
ΔH= 850 kJ/mol
Fe2O3 + 2Al
2Fe + Al2O3
Reactants
Fe2O3 + 2Al
Enthalpy
ΔH = H(products) - H(reactants)
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Fe2O3 + 2Al
Thermite
Enthalpy Diagram
Reactants
Enthalpy
Enthalpy
ΔH= -850 kJ/mol
Fe2O3 + 2Al
2Fe + Al2O3
Products
2Fe + Al2O3
Enthalpy
Hess’s Law
!
ΔH = H(products) - H(reactants)
!
Reverse reaction - Reverse sign
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Ammonium nitrate
Endothermic reaction
Energy Diagram
Energy
Products
Reactants
ΔH
l
a
h
nt
E
n
o
i
act
e
r
f
o
y
p
NH4NO3(s)
NH4+(aq) + NO3-(aq)
Reaction Progress
ΔH = H(products) - H(reactants)
ΔH = 365kJ/mol
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Enthalpy
NH4+(aq) + NO3-(aq)
Ammonium nitrate
Enthalpy Diagram
Products
Enthalpy
NH4NO3(s)
ΔH= 365 kJ/mol
NH4+(aq) + NO3-(aq)
Reactants
NH4NO3(s)
Enthalpy
ΔH = H(products) - H(reactants)
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Born–Haber cycle
Hess’s Law
!
!
Enthalpy of reaction is equal to the sum of the parts
F2(g)
Li(s)
LiF(s)
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C(s) + O2(g)
CO(g) + ½O2(g)
CO2(g)
CO2(g)
ΔH = -283.0 kJ
Hess’s Law
Target
C(s) + ½O2(s)
ΔH = -393.5 kJ
!
CO(g)
!
Reverse sign
The sum of the parts
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C(s) + O2(g)
CO2(g)
CO2(g)
ΔH = -393.5 kJ
CO(g)+½O2(g)
ΔH = 283.0 kJ
C(s) + ½O2(g)
CO(g)
ΔH = -110.5 kJ
Hess’s Law
!
Target
C(s) + ½O2(s)
!
CO(g)
Reverse sign
The sum of the pars
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NO(g)+O3(g)
O3(g)
O2(g)
NO2(g)+ O2(g)
3
O
(g)
2
2
2O(g)
ΔH = -198.9 kJ
ΔH = -142.3 kJ
ΔH = 495.0 kJ
Target
NO(g) + O(g)
NO2(g)
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NO(g)+O3(g)
3
O
(g)
2
2
2O(g)
NO2(g)+ O2(g)
O3(g)
O2(g)
ΔH = -198.9 kJ
ΔH = 142.3 kJ
ΔH = -495.0 kJ
Target
NO(g) + O(g)
NO2(g)
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NO(g)+O3(g)
3
O
(g)
2
2
½( 2O(g)
NO2(g)+ O2(g)
O3(g)
O2(g) )
ΔH = -198.9 kJ
ΔH = 142.3 kJ
ΔH = -495.0 kJ
Target
NO(g) + O(g)
NO2(g)
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NO(g)+O3(g)
3
O
(g)
2
2
O(g)
NO(g) + O(g)
NO2(g)+ O2(g)
O3(g)
½O2(g)
NO2(g)
ΔH = -198.9 kJ
ΔH = 142.3 kJ
ΔH = -247.5 kJ
ΔH = -304.1 kJ
Target
NO(g) + O(g)
NO2(g)
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Did you learn?
Enthalpy of
Reaction
Reactants
Products
Bond Energies
- Bond Energies
To draw qualitative and quantitative patterns in
reaction enthalpy and the energies involved in
breaking and forming chemical bonds.
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Acknowledgements
Dnn87. Pieces of Lithium Metal from the Dennis S.k Collection, 12/12-07. Self-photographed. http://commons.wikimedia.org/wiki/File:Limetal.JPG.
“File:AlfredNobel Adjusted.jpg,” December 16, 2013. http://en.wikipedia.org/wiki/File:AlfredNobel_adjusted.jpg.
“File:Dynamite-5.svg,” December 16, 2013. http://en.wikipedia.org/wiki/File:Dynamite-5.svg.
“File:Hess Germain Henri.jpg,” December 22, 2013. http://en.wikipedia.org/wiki/File:Hess_Germain_Henri.jpg.
“File:Nitroglycerin-3D-vdW.png,” December 16, 2013. http://en.wikipedia.org/wiki/File:Nitroglycerin-3D-vdW.png.
“File:ThermiteReaction.jpg,” December 11, 2013. http://en.wikipedia.org/w/index.php?title=File:ThermiteReaction.jpg&oldid=543297076.
Haacken, User: Herbert. English: Instant Cold Pack, March 15, 2012. Own work: Herbert Haacken. http://commons.wikimedia.org/wiki/File:2012-03-15_Ruck-Zuck-Pack_K%C3%A4lte_Katalog_Small.gif.
V1adis1av. Single Crystal of Lithium Fluoride, LiF, in a Beaker with Water, March 20, 2008. Own work. http://commons.wikimedia.org/wiki/File:LiF-crystal.jPeG.
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