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# Energy Diagrams I - PowerPoint PPT Presentation

Energy Diagrams I. Dr. Rusay Fall 2004. A Reaction Coordinate Diagram. Gibbs standard free energy change ( D G o ). Enthalphy ( D H o ): the heat given off or absorbed during a reaction. Entropy ( D S o ): a measure of freedom of motion. Thermodynamic Quantities.

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### Energy Diagrams I

Dr. Rusay

Fall 2004

Enthalphy (DHo): the heat given off or absorbed

during a reaction

Entropy (DSo): a measure of freedom of motion

Thermodynamic Quantities

DGo = DHo - TDSo

DG,DH,DS,DE are state functions

E = q + w

H = qp

If DSo is small compared to DHo, DGo ~ DHo

Example: PhotosynthesisEnergy Capture (Endergonic Reaction)

n CO2(g) + n H2O(g) + energy 

PhotosynthesisEnergy Capture (Endergonic Reaction)

n CO2(g) + n H2O(g) + energy 

PhotosynthesisEnergy Capture (Endergonic Reaction)

n CO2(g) + n H2O(g) + energy  (CH2O) n (aq) + n O2(g)

An Endothermic (Endergonic) Reaction

Exothermic Reactions : Energy Release

2 C8H18 + 25 O2 16 CO2 + 18 H2O

Exothermic Reactions : Energy Release

2 C8H18 + 25 O2 16 CO2 + 18 H2O

Exothermic Reactions : Energy Release

2 C8H18 + 25 O2 16 CO2 + 18 H2O

An Exothermic (Exergonic) Reaction

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?

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