Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation...
-
Upload
mark-golden -
Category
Documents
-
view
225 -
download
0
Transcript of Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation...
![Page 1: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/1.jpg)
Heats of Combustion,Heats of Formation,
Heats of Hydrogenationand
Bond Dissociation Energies
![Page 2: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/2.jpg)
Germain Henri Hess
(1802 - 1850)
Hess’s Law (1840)
• The total heat liberated in a series of chemical reactions is equal to the sum of the heats liberated in the individual steps.
• The heat liberated, Ho, (enthalpy) is a state function.
•State functions are independent of path.
![Page 3: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/3.jpg)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
New Haven
ChicagoDenver
SanFrancisco
Dallas
Miami
The “Heat” Liberated in Either Route is the Same
![Page 4: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/4.jpg)
The Standard State is the zero point for chemical reactions.
A temperature of 298oK and 1 atmosphere pressure
Carbon as graphite
Hydrogen as a gas
Oxygen as a gas
Chlorine as a gas
Bromine as a liquid
Ho = 0 kcal/mol
![Page 5: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/5.jpg)
Combustion of Graphite and Hydrogen at 298oK
1C, O2
CO2
carbon dioxide
-94.0 kcal/mol
H2, 1/2O2
H2O liquid water
-68.3 kcal/mol
![Page 6: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/6.jpg)
Combustion of Methane
2H2, O2
2H2O liquid water
Combustion of H2
2x(-68.3)=-137.6 kcal/mol
combustion of methaneHo = -213.7 kcal/mol
C, 2H2
CH4
Hfo = -17.9 kcal/mol
-94.0 kcal/mol
1C, O2
CO2
carbon dioxide
sum = -231.6 kcal/mol
-137.6 kcal/mol
![Page 7: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/7.jpg)
Hfo of Methanol and Its Products of Oxidation
1C, 2H2, 1/2O21C, H2, 1/2O21C, H2, O2 1C, O2
CH3OHmethanol(l)
-57.4 kcal/mol
CH2Oformaldehyde(g)
-26.0 kcal/mol
CO2
carbon dioxide
-94.0 kcal/mol
HCO2H formic acid(l)
-101.6 kcal/mol
![Page 8: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/8.jpg)
Not All Compounds Are More Stable Than Their Elements
acetylene
C2H2
2CO2 + H2O
Ho(comb)
= -310.6 kcal/mol
Hfo = +54.3
kcal/mol2C + H2
Ho(comb)
= -256.3 kcal/mol
![Page 9: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/9.jpg)
Combustion of Hexane Constitutional Isomers
Hfo = -39.9
kcal/molHf
o = -41.1 kcal/mol
Hfo = -44.5
kcal/mol
6C + 7H2
6CO2 + 7H2O Ho (comb)
= -1,042 kcal/mol
Hcombo
Hcombo
Hcombo
![Page 10: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/10.jpg)
Heats of Hydrogenation
Ho(H2)
= -27.3 kcal/mol
Hfo = -30.0
kcal/mol
Ho(H2)
= -28.3 kcal/mol
1.0 kcal/mol
Ho(H2)
= -30.0 kcal/mol
Hfo = 0.0
kcal/molstandard state
Hfo = -1.7
kcal/molHf
o = -2.7 kcal/mol
![Page 11: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/11.jpg)
DHo (RH)
(R. + H
.)
Hfo
(RH)
Hfo
(R.)
Hfo
(H.)
Bond Dissociation Energy (BDE)
Hfo
(H.)
DHo (RH) = Hfo (H.) + Hf
o (R.) - Hf
o (RH)
![Page 12: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/12.jpg)
80
90
100
110
120
130
140
0 1 2 3 4C-spC-sp C-sp2 C-sp3 C-sp
DHo (kcal/mol)
C-H
C-C(sp3)
HCCH
CH2CH2
Carbon Hybridization
Bond Dissociation Energy and Hybridization
CH3CH3
![Page 13: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/13.jpg)
50
60
70
80
90
100
110
0 1 2 3 4 5Me Me Mei-Pr t-Bu MeEt
I
Br
Cl
t-Bu
H
Et Me
i-Pr
DHo (kcal/mol)
Alkyl Substituent
BDEs of C-C, C-X and C-H Bonds
![Page 14: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/14.jpg)
78
80
82
84
86
88
90
92
1.52 1.53 1.54 1.55 1.56 1.57 1.58
Bond Length (Angstroms)
DHo (kcal/mol)
CH3CH3
(CH3)3CC(CH3)3
C-C Bond Strength vs. Bond Length
![Page 15: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/15.jpg)
2025
32
40
90 89 88.6 87.5
35 35 35 353529
21.6
12.5
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4
C-C Bonds
BDE
Hf R-R’ Hf Radical 1 Hf Radical 2
Ho (kcal/mol)
Me-Me Me-Et Me-iPr Me-tBu tBu-tBu
![Page 16: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/16.jpg)
Butane Isomers
30 30 32 32
101 99 10197
52 52 52 52
19 17 1713
0
20
40
60
80
100
120
1 2 3 4
BDE
Hf R-H Hf H atom Hf R radical
n-Bu 1o n-Bu 2o i-Bu 1o i-Bu 3o
Ho (kcal/mol)
![Page 17: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/17.jpg)
Formation of C4-C18 Even Primary Radicals from Their n-Alkanes
-30-40
-50-60
-70-80
-90-100
101 101 101 101 101 101 101 101
52 52 52 52 52 52 52 52
199
-1-11
-21-31
-41-51
-150
-100
-50
0
50
100
150
Hf(RH)
BDE
Hf(H atom)
Hf(R radical)
Ho (kcal/mol)
Hf R radical Hf H atom
Hf R-H BDE
![Page 18: Title Heats of Combustion, Heats of Formation, Heats of Hydrogenation and Bond Dissociation Energies.](https://reader036.fdocuments.net/reader036/viewer/2022062304/56649ce45503460f949b1634/html5/thumbnails/18.jpg)
The End