Discussion Exercise 8: Redox Reactions and Quantitative Thermodynamics
Skill 1: Recognize redox reactions
 If the net oxidation numbers of a product increase (more positive, less negative) from
reactant, then the compound has been oxidized
 If the net oxidation numbers of a product decrease (less positive, more negative) from
reactant, then the compound has been reduced
 If the net oxidation numbers remain unchanged, then it is not a redox reaction
Strategy for problem solving:
1. Identify all carbon atoms that have changed
2. Determine their oxidation numbers by assigning -1 for each C-H bond and +1 for every
C-O or C-N bond.
3. Determine if there is a net change in oxidation numbers.
Examples:
Problem 1: Label each reaction as oxidation, reduction, or neither.
Problem 2: The following reaction sequence is part of the citric acid cycle. Are either of these
reactions redox reactions?
Skill 2: Use redox reactions to predict spontaneity and need for cofactor
 If a metabolite is oxidized, the metabolite loses potential energy.
o Oxidation of metabolites releases energy that can be used to reduce a cofactor
o Oxidation requires a cofactor to be reduced: NAD+  NADH or FAD  FADH2
 If a metabolite is reduced, the metabolite gains potential energy.
o Reduction of metabolites requires energy from a reactive cofactor
o Reduction requires a cofactor to be oxidized: NADH  NAD+ or FADH2 
FAD
Problem 3: The following are four steps in fatty acid biosynthesis. Is it a reductive or oxidative
process? Which steps require cofactors?
Problem 4: Under anaerobic conditions, pyruvate is converted to lactate. What type of reaction is this? What cofactor is needed? H3C
O
O
C
C
cofactor and H+
O
-
H3C
OH
O
C
H
C
O-
Skill 3: Quantitative thermodynamics
 Standard free energy is the measure of spontaneity under standard conditions
o Standard free energy reflects the potential of bonds
o Equilibrium concentrations can be determined from standard free energy
 Free energy is the measure of spontaneity under any conditions
o Free energy reflects the potential of bonds and the concentrations of reactants and
products
o Free energy can be used to determine concentrations of products and reactants
under current conditions
Problems: Refer to the text to solve these problems:
Chapter 15, #30
Chapter 15, #31
Chapter 16, #21