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📌 Illustrated Diagram: Galvanic Cell Logic

Electrochemistry – Complete CBSE Class 12 Chemistry Notes

Unit 2 | Electrochemistry | CBSE 2026–27

1. Galvanic and Electrolytic Cells

Remember: oxidation is always at the anode and reduction is always at the cathode; the sign of the electrodes depends on the cell type.

2. Standard Cell Potential

E°cell = E°cathode − E°anode. For E°cathode = +0.34 V and E°anode = −0.76 V, E°cell = 1.10 V.

3. Nernst Equation

At 298 K: E = E° − (0.0591/n) log Q. Here n is the number of electrons transferred and Q is the reaction quotient.

Worked Example

For a reaction involving n = 2 and Q = 100, the correction term is (0.0591/2)log100 = 0.0591 V. Hence E = E° − 0.0591 V.

4. Conductance

Resistance R and conductance G are reciprocals: G = 1/R. Conductivity and molar conductivity incorporate cell geometry and concentration respectively. Always check units before substituting values.

5. Kohlrausch’s Law

At infinite dilution, limiting molar conductivity can be expressed as the sum of contributions from individual ions. This helps estimate values that are difficult to determine directly.

6. Faraday’s Laws

The amount of substance liberated at an electrode is proportional to the quantity of electricity passed. Since Q = It, current and time can be connected to deposited mass.

7. Batteries, Fuel Cells and Corrosion

• Primary cell: generally not conveniently rechargeable.
• Secondary cell: rechargeable.
• Fuel cell: reactants are continuously supplied.
• Corrosion: electrochemical oxidation of a metal; prevention includes coating, alloying and cathodic protection.

🧠 Cell Diagram

📝 Competency Practice

1. Why does a salt bridge help a galvanic cell continue operating?
2. Two students reverse anode and cathode signs while calculating E°cell. Identify the conceptual error.
3. Explain why a catalyst is unrelated to the value of standard cell potential.
4. Why does corrosion accelerate under conditions that favour electrochemical reactions?

🎯 Board Numericals

1. Calculate E°cell from two standard electrode potentials.
2. Use the Nernst equation to calculate cell potential under non-standard conditions.
3. Calculate molar conductivity from resistance, cell constant and concentration data.
4. Calculate mass deposited using current and time.

MCQs

1. Oxidation occurs at the anode in both cell types. True.
2. Reduction occurs at the cathode. True.
3. E°cell is obtained by cathode potential minus anode potential. True.
4. Increasing Q always leaves the Nernst correction unchanged. False.

Deep-Dive: Electrochemical Cells

Galvanic Cell

A galvanic cell converts spontaneous redox energy into electrical energy. Oxidation occurs at the anode and reduction at the cathode. Electrons travel through the external circuit from anode to cathode.

Nernst Equation

At 298 K, E=E°−(0.0591/n)log Q. The reaction quotient Q must be written using the appropriate activities/concentrations.

Worked Numerical

For a cell with E°=1.10 V, n=2 and Q=10, E=1.10−(0.0591/2)log10≈1.070 V.

Conductivity

Conductance G=1/R. Conductivity κ is related to conductance and cell constant. Molar conductivity increases on dilution because ions experience less interionic interaction.

Batteries, Fuel Cells & Corrosion

Know the working principle and electrode processes of common cells in the syllabus. Corrosion is an electrochemical oxidation process; prevention includes coating, alloying and cathodic protection.

Common Mistakes

• Reversing anode/cathode rules between galvanic and electrolytic contexts.
• Using Q incorrectly in the Nernst equation.
• Mixing conductance, conductivity and molar conductivity.

Practice

1. Write cell notation and identify electrodes.
2. Calculate E using the Nernst equation.
3. Relate ΔG° and E°.
4. Solve conductivity and molar-conductivity numericals.

Electrochemistry — Concept Map

Cell Potential

For a galvanic cell, E°_cell=E°_cathode−E°_anode. A positive standard cell potential corresponds to a thermodynamically spontaneous cell reaction under standard conditions.

Nernst Equation

At 298 K, E=E°−(0.0591/n)log Q. Identify n as the number of electrons transferred in the balanced overall reaction.

Worked Numerical

For a cell with E°=1.10 V, n=2 and Q=10, E=1.10−(0.0591/2)log10≈1.070 V at 298 K.

Conductance

Understand resistance, conductance, conductivity and molar conductivity as distinct quantities. Molar conductivity generally increases on dilution because ions experience greater freedom of movement.

Electrolysis

Faraday’s laws connect the quantity of electricity passed through an electrolyte with the amount of substance deposited or liberated.

CBSE Application Practice

1. Calculate Ecell using standard electrode potentials.
2. Use the Nernst equation for non-standard conditions.
3. Determine ΔG° from E°cell.
4. Calculate deposited mass using Faraday’s law.
5. Interpret conductivity versus concentration data.