SectionC12_BB(1) - Tagged

Introduction to Redox Processes

• Chemistry for Bioscientists I Section C12 Redox

• University of Manchester, 1824

Fundamental Reactions

Photosynthesis and Cellular Respiration

• 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 and Reduction

Definition of Terms

• Oxidation: Loss of electrons

• Reduction: Gain of electrons

• Redox Reaction: Involves loss of electrons from one species and gain by another

Agents in Redox Reactions

• Reducing Agent: Acts as an electron donor and is itself oxidized

• Oxidizing Agent: Acts as electron acceptor and is reduced

Common Redox Processes

Examples

1. In Respiration:

   • Glucose (C6H12O6) is oxidized to produce carbon dioxide and water.

2. In Photosynthesis:

   • Carbon dioxide (6CO2) is reduced to produce glucose (C6H12O6).

3. In Corrosion:

   • Example: 2Fe(s) + O2 + 4H+ → 2Fe2+ + 2H2O

   • Each iron (Fe) atom loses 2 electrons (oxidized).

Redox Processes and Coenzymes

Electron Carriers

• NAD+ and FAD:

  • NAD+ → NADH + H+ + 2e⁻ (Oxidation of ethanol by alcohol dehydrogenase)

  • FAD + 2H+ + 2e⁻ → FADH2

Electrochemistry

Definitions and Concepts

• Electrochemistry: Study of chemical processes that cause electrons to move.

  • Allows quantification of oxidizing and reducing power.

  • Thermodynamic quantities: A, G, & AS

Half-Reactions

• 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-Cells in Electrochemical Systems

Concepts

• Half-Reactions: Theoretical descriptions facilitating electron transfer.

• Redox Couple: Oxidised (Ox) vs Reduced (Red) species.

Setup of Half-Cells

• 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)

Electrochemical Cells

Types

• Voltaic (Galvanic) Cell: Generates current spontaneously.

• Electrolytic Cell: Requires external voltage to drive a reaction.

Cell Setup

• 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)

Conclusion

• Summary of important concepts in redox chemistry relevant to biosciences and implications for biological systems.