Energy Diagrams I Dr. Rusay Fall 2004

A Reaction Coordinate Diagram

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

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

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

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

Burning Gasoline (Octane) Exothermic Reactions : Energy Release 2 C8H18 + 25 O2  16 CO2 + 18 H2O

Burning Gasoline (Octane) Exothermic Reactions : Energy Release 2 C8H18 + 25 O2  16 CO2 + 18 H2O

Burning Gasoline (Octane) Exothermic Reactions : Energy Release 2 C8H18 + 25 O2  16 CO2 + 18 H2O An Exothermic (Exergonic) Reaction

Burning Gasoline (Octane) Exothermic Reactions : Energy Release 2 C8H18 + 25 O2  16 CO2 + 18 H2O  H 16 CO2 + 18 H2O (Products are all the same.) Are isomers the same thermodynamically?

Burning Gasoline (Octane) Exothermic Reactions : Energy Release 2 C8H18 + 25 O2  16 CO2 + 18 H2O A B C  H D 16 CO2 + 18 H2O (Products are all the same.) Which isomers are more stable thermodynamically? D > C > B > A