1. Thermodynamics
Chemical reactions proceed according to the rules of thermodynamics
The law of conservation of energy – energy can be converted from one form to another but the total amount of energy is constant
Entropy – the universe is becoming more chaotic
ACK!

2. Gas constant: R = 8.315 Joules/K* mol or
Thermodynamics
Some constants
Gas constant: R = Joules/K* mol or
cal/K.mol
Faradays constant: F = Joules/Volt.mol or
23062 cal/Volt* mol

3. Energy: definitions
Energy – ability to do work
Energetics – energy transfer
Types of energy
Potential – trapped energy
Kinetic – energy of movement

4. Energy Categories: more definitions
Radiant energy – energy released from one object to another
Mechanical energy – energy to move objects from place to place
Electrical energy – energy that results from the movement of charged particles down a charge gradient
Thermal energy – reflected in the movement of particles and serves to increase temperature
Chemical energy – energy that is held within chemical bonds

5. Energy Categories, Cont.
Animals rely on all five types of energy, which are interconvertible

6. Food Webs are Transfers of Energy
Figure 2.3

7. Thermodynamics in a biological setting
Free Energy (G)
1. Change in free Energy (ΔG)
ΔG = Products – Reactants
ΔG negative – reaction will proceed forward →
ΔG positive – reaction will proceed backward ←
ΔG zero – reaction at equilibrium ↔
2. Standard free Energy – ΔGo: 298 K (25oC), 1 atm pressure, pH 7.0 and 1M [initial] for all reactants and products

8.  Thermal energy   movement of molecules
Most chemical reactions involve changes in thermal energy
Exothermic reactions – release heat
Endothermic reactions – absorb heat

9. Chemical Reactions and Thermal Energy
Enthalpy
Enthalpy – average thermal energy of a collection of molecules i.e. bond energy
Change in enthalpy (DH) = Hproducts – Hsubstrates
Exothermic: DH is negative i.e. C6H12O6 + 6O → 6CO2 + 6H2O + energy
Endothermic: DH is positive i.e. ADP + Pi → ATP

10. Chemical Reactions and Thermal Energy
Enthalpy and Entropy together
Entropy (S) – measure of randomness or disorder
Exothermic: DH is negative, increase in DS → reaction will occur spontaneously – negative DG
Endothermic: DH is positive, DS is positive → reaction will occur spontaneously. It has to overcome the positive DH

11. Free Energy: calculations
Free energy changes of reactions are additive (coupled reactions):
Consider the phosphorylation of glucose to glucose 6-phosphate:
DGo: glucose + Pi ↔ glucose-6-phosphate + H2O = 3.3 kcal/mol
DGo: ATP + H2O ↔ ADP + Pi = -7.3 kcal/mol
Summing these reactions together: ATP + glucose ↔ ADP + glucose 6-phosphate  
DG° = (-7.3) = - 4kcal/mol (favourable)

12. DG = DGo + RTln ([products]/[reactants])
Biological reactions
DG = DGo + RTln ([products]/[reactants])
Where R = gas constant, T = temperature in Kelvin
Example:
glucose + ATP ↔ glucose-6-phosphte + ADP
DGo: glucose + Pi ↔ glucose-6-phosphate + H2O = 3.3 kcal/mol
DGo: ATP + H2O ↔ ADP + Pi = -7.3 kcal/mol
Glucose: [5mM]; ATP: [2mM]; ADP: [0.15mM]; glucose-6-phosphate: [0.05mM]
So, DG = kcal/mol cal/K mol)(298K)ln((0.05*0.15)/(5*2))
= -8.26kcal/mol
Recall DG = products - reactants

13. ΔG for reactions that don’t make or break bonds
DGo is zero
- Examples: glucose transport, ion transport across membranes
DG = RTln ([inside]/[outside])
Or for charged ions:
DG = RTln ([inside]/[outside]) + zFEm
where z = valence of the ion; F = Faraday constant and Em = membrane potential

14. Transport across membranes
DG = RTln ([inside]/[outside]) + zFEm
where z = valence of the ion; F = Faraday constant and Em = membrane potential
Example: Diffusion of Cl- from out to in
Cl- outside cell: 120mM; Cl- inside cell: 10mM; Em = -80mV
DG = (1.987cal/K mol)(298K)(ln(10/120) + (-1)(23062 cal/V mol)(-0.08V) =
376 cal/mol