Chemistry for Bioscientists I Section C12 Redox
University of Manchester, 1824
Photosynthesis Reaction: 6CO2 + 6H2O → C6H12O6 + 6O2
Converts carbon dioxide and water into glucose and oxygen using sunlight.
Combustion of Glucose (Aerobic Respiration):
Reaction: C6H12O6 + 6O2 → 6CO2 + 6H2O
Enthalpy change (ΔG°) is -2870 kJ·mol⁻¹ (25°C/1atm)
Oxidation: Loss of electrons
Reduction: Gain of electrons
Redox Reaction: Involves loss of electrons from one species and gain by another
Reducing Agent: Acts as an electron donor and is itself oxidized
Oxidizing Agent: Acts as electron acceptor and is reduced
In Respiration:
Glucose (C6H12O6) is oxidized to produce carbon dioxide and water.
In Photosynthesis:
Carbon dioxide (6CO2) is reduced to produce glucose (C6H12O6).
In Corrosion:
Example: 2Fe(s) + O2 + 4H+ → 2Fe2+ + 2H2O
Each iron (Fe) atom loses 2 electrons (oxidized).
NAD+ and FAD:
NAD+ → NADH + H+ + 2e⁻ (Oxidation of ethanol by alcohol dehydrogenase)
FAD + 2H+ + 2e⁻ → FADH2
Electrochemistry: Study of chemical processes that cause electrons to move.
Allows quantification of oxidizing and reducing power.
Thermodynamic quantities: A, G, & AS
A redox reaction can be split into two half-reactions to show electron loss and gain.
Example of displacement reaction:
Cu²⁺ + Zn → Cu + Zn²⁺ (Reduction and Oxidation steps)
Half-Reactions: Theoretical descriptions facilitating electron transfer.
Redox Couple: Oxidised (Ox) vs Reduced (Red) species.
Electrons flow from the oxidation half-reaction to the reduction half-reaction.
Example setup between zinc metal and copper metal in respective sulfate solutions:
Zn → Zn²⁺ + 2e⁻ (Oxidation)
Cu²⁺ + 2e⁻ → Cu (Reduction)
Voltaic (Galvanic) Cell: Generates current spontaneously.
Electrolytic Cell: Requires external voltage to drive a reaction.
Daniell Cell: Key setup illustrating oxidation and reduction reactions, showing electron flow through a circuit with a salt bridge for charge balance.
Oxidation occurs at the anode, reduction occurs at the cathode.
Zn → Zn²⁺ + 2e⁻ (Anode)
Cu²⁺ + 2e⁻ → Cu (Cathode)
Summary of important concepts in redox chemistry relevant to biosciences and implications for biological systems.