Electrode Reactions – LEOGER

Dr E. Ramanathan PhD

Video

Notes:

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Electrochemistry – Class Notes

1. Introduction

• Electrochemistry is the study of the relationship between chemical energy and electrical energy.
• It is broadly divided into:
  • Electrolytics – Study of reactions in electrolytes (solutions that conduct electricity).
  • Electrodics – Study of reactions occurring on the surface of electrodes.

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2. Redox Reactions

• Oxidation:
  • Occurs at the anode
  • Involves:
    • Addition of oxygen
    • Removal of hydrogen
    • Loss of electrons
    • Increase in oxidation number
  • Mnemonics:
    • LEO – Loss of Electrons is Oxidation
    • OIL – Oxidation Is Loss
• Reduction:
  • Occurs at the cathode
  • Involves:
    • Removal of oxygen
    • Addition of hydrogen
    • Gain of electrons
    • Decrease in oxidation number
  • Mnemonics:
    • GER – Gain of Electrons is Reduction
    • RIG – Reduction Is Gain

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3. Electrode Reactions

• Anode – Site of oxidation
• Cathode – Site of reduction
• Example:
  • Zn → Zn²⁺ + 2e⁻ → Oxidation at Anode
  • O + 2e⁻ → O²⁻ → Reduction at Cathode

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4. Driving Force – Electrode Potential

• Reduction Potential (Eᵣₑd): Tendency of a species to gain electrons.
• Oxidation Potential (Eₒₓ): Tendency to lose electrons.
• Standard electrode potential is measured as reduction potential by convention.

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5. Electromotive Force (EMF)

• EMF of a cell (E_cell):

• It determines the spontaneity of the reaction.
• If Ecell>0E_{\text{cell}} > 0, the reaction is spontaneous.

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6. Galvanic Cell Representation

• General format:

• Where:
  • Left side = Anode (oxidation)
  • Right side = Cathode (reduction)
  • Double slash // = Salt Bridge

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7. Salt Bridge

• A U-shaped tube containing an inert electrolyte (e.g., KCl, KNO₃) in gel form.
• Maintains electrical neutrality by allowing ion flow.
• Prevents direct mixing of solutions, thereby completing the circuit.

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8. Example Reactions

• Fe²⁺ → Fe³⁺ + e⁻ (Oxidation)
• Fe³⁺ + e⁻ → Fe²⁺ (Reduction)
• Zn → Zn²⁺ + 2e⁻ (Oxidation)
• O₂ + 4e⁻ → 2O²⁻ (Reduction)

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9. Summary

• Redox reactions are essential for electrochemical processes.
• EMF, salt bridge, electrode potentials, and proper cell representation are fundamental to understanding galvanic and electrolytic cells.

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Worksheets

Fill in the blanks

1. Oxidation is the _____ of electrons.
2. Reduction is the _____ of electrons.
3. A redox reaction involves both _____ and reduction.
4. The substance that gets reduced is called the _____ agent.
5. The substance that gets oxidized is called the _____ agent.
6. In electrochemical cells, electrons flow from _____ to cathode.
7. The electrode where oxidation occurs is the _____.
8. The electrode where reduction occurs is the _____.
9. The standard electrode potential of hydrogen is defined as _____ volts.
10. A galvanic cell converts _____ energy into electrical energy.
11. An electrolytic cell converts electrical energy into _____ energy.
12. The Nernst equation relates electrode potential to _____ concentration.
13. The salt bridge maintains _____ neutrality in the cell.
14. Standard conditions are 1 M concentration, 1 atm pressure, and _____°C temperature.
15. The flow of electrons in a circuit is from _____ potential to higher potential.
16. In a Daniel cell, _____ is oxidized.
17. In a Daniel cell, copper is _____.
18. The standard reduction potential of a species measures its tendency to get _____.
19. A more positive electrode potential indicates a stronger _____ agent.
20. Electrochemical cells are governed by the _____ free energy change.

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