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.

robot