1. Energy Diagrams I
Dr. Rusay
Fall 2004

2. A Reaction Coordinate Diagram

3. Thermodynamic Quantities
DGo = DHo - TDSo
DG,DH,DS, DE are state functions
E = q + w
H = qp
Gibbs standard free energy change (DGo)
Enthalphy (DHo): the heat given off or absorbed
during a reaction
Entropy (DSo): a measure of freedom of motion
If DSo is small compared to DHo, DGo ~ DHo

4. Example: Photosynthesis Energy Capture (Endergonic Reaction)
n CO2(g) + n H2O(g) + energy 

5. Photosynthesis Energy Capture (Endergonic Reaction)
n CO2(g) + n H2O(g) + energy 

6. Photosynthesis Energy Capture (Endergonic Reaction)
n CO2(g) + n H2O(g) + energy  (CH2O) n (aq) + n O2(g)
An Endothermic (Endergonic) Reaction

7. Burning Gasoline (Octane)
Exothermic Reactions : Energy Release
2 C8H O2  16 CO H2O

8. Burning Gasoline (Octane)
Exothermic Reactions : Energy Release
2 C8H O2  16 CO H2O

9. Burning Gasoline (Octane)
Exothermic Reactions : Energy Release
2 C8H O2  16 CO H2O
An Exothermic (Exergonic) Reaction

10. Burning Gasoline (Octane)
Exothermic Reactions : Energy Release
2 C8H O2  16 CO H2O
 H
16 CO H2O
(Products are all the same.)
Are isomers the same thermodynamically?

11. Burning Gasoline (Octane)
Exothermic Reactions : Energy Release
2 C8H O2  16 CO H2O A B C
 H D
16 CO H2O
(Products are all the same.)
Which isomers are more stable thermodynamically?
D > C > B > A