Electrochemistry Class 12 Notes PDF | Nernst Equation, EMF & Numericals Guide

Mastering the concepts of electrochemical cells and conductance is non-negotiable for anyone aiming for a top rank in NEET. This electrochemistry class 12 notes pdf guide provides a deep dive into the transformation between chemical and electrical energy. From calculating cell EMF to understanding molar conductance, we cover the quantitative and theoretical aspects that frequently appear in competitive exams.

01
Introduction to Electrochemistry

Electrochemistry is the study of production of electricity from energy released during spontaneous chemical reactions and the use of electrical energy to bring about non-spontaneous chemical transformations. It is fundamentally based on redox reactions—the simultaneous occurrence of oxidation and reduction.

SPONTANEOUS REDOX Chemical energy is converted into electrical energy (e.g., Galvanic Cells).

NON-SPONTANEOUS REDOX Electrical energy is used to drive chemical changes (e.g., Electrolytic Cells).

02
Electrochemical Cells

An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or facilitating chemical reactions through the introduction of electrical energy.

Feature	Galvanic (Voltaic) Cell	Electrolytic Cell
Energy Conversion	Chemical to Electrical	Electrical to Chemical
Spontaneity	Spontaneous (ΔG < 0)	Non-spontaneous (ΔG > 0)
Anode Charge	Negative (−)	Positive (+)
Cathode Charge	Positive (+)	Negative (−)

03
Galvanic Cell: Construction and Working

In a Galvanic cell, two half-cells are connected. Each half-cell consists of a metal electrode dipped in its salt solution. A **Salt Bridge**—containing an inert electrolyte like KCl or KNO₃—completes the circuit and maintains electrical neutrality.

CELL REPRESENTATION (IUPAC)

Anode | Anode Ion (conc) || Cathode Ion (conc) | Cathode

TIP

Remember the acronym **LOAN**: **L**eft side, **O**xidation, **A**node, **N**egative electrode. This applies to Galvanic cells!

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04
Electrode Potential and SHE

Electrode potential is the potential difference developed between the electrode and its electrolyte. To measure the absolute potential of a single electrode, we use a reference called the **Standard Hydrogen Electrode (SHE)**.

Standard Hydrogen Electrode (SHE): E° = 0.00 V (at 298 K, 1 bar H₂, 1 M H⁺)

05
Electrochemical Series

This is a list of electrodes arranged in decreasing order of their standard reduction potentials. In your electrochemistry class 12 notes pdf study plan, this series is the primary tool for predicting feasibility.

REACTIVITY PREDICTION A metal with a lower reduction potential can displace a metal with a higher reduction potential from its salt solution.

OXIDIZING POWER The more positive the E° value, the stronger the oxidizing agent (e.g., F₂).

06
EMF of a Cell

The Electromotive Force (EMF) is the potential difference between two electrodes when no current is flowing through the cell. It is always calculated using standard reduction potentials.

EMF CALCULATION

E°_cell = E°_cathode − E°_anode

WARN

Always use **Reduction Potentials** in the formula. If an Oxidation Potential is given, change its sign to convert it to Reduction Potential before calculating E°_cell.

07
Nernst Equation

The Nernst Equation relates the cell potential to the concentration of ions. It allows us to calculate EMF under non-standard conditions, which is a frequent NEET numerical area.

E_cell = E°_cell − (0.0591 / n) log([Products] / [Reactants]) (at 298 K)

Relationship with Gibbs Free Energy

The electrical work done by the cell is equal to the decrease in Gibbs free energy.

THERMODYNAMIC LINK

ΔG = −nFE_cell | ΔG° = −nFE°_cell

08
Conductance of Electrolytic Solutions

Electrolytic conductance is the ease with which current flows through an electrolytic solution. Unlike metallic conductors, electrolytic conductance increases with temperature.

Term	Symbol	Unit
Specific Conductance (Conductivity)	κ (kappa)	S m⁻¹ or S cm⁻¹
Molar Conductance	Λ_m	S cm² mol⁻¹
Cell Constant	G*	cm⁻¹

Λ_m = (κ × 1000) / Molarity

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09
Kohlrausch’s Law

Kohlrausch’s Law states that the limiting molar conductivity of an electrolyte is the sum of the individual contributions of the anion and cation. This is essential for calculating the conductivity of weak electrolytes in your electrochemistry class 12 notes pdf revision.

KOHLRAUSCH’S EXPRESSION

Λ°_m = v₊λ°₊ + v₋λ°₋

10
Faraday’s Laws of Electrolysis

Faraday’s laws provide the quantitative aspect of electrolysis. They relate the amount of substance deposited to the quantity of electricity passed through the cell.

FIRST LAW The mass of substance deposited (w) is directly proportional to the quantity of electricity (Q).
w = ZIt

SECOND LAW If the same amount of electricity is passed through different electrolytes, the masses deposited are proportional to their chemical equivalent weights.

11
Batteries, Fuel Cells, and Corrosion

Batteries are galvanic cells where chemical energy is stored. Fuel cells, like the H₂-O₂ fuel cell, are highly efficient and eco-friendly as they produce only water as a byproduct.

Fuel Cell Reaction: 2H₂ + O₂ → 2H₂O | High Efficiency (~70%)

Corrosion: Electrochemical Rusting

Rusting of iron is an electrochemical process. At the anode, Fe is oxidized to Fe²⁺. At the cathode, oxygen is reduced in the presence of H⁺ ions.

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Quick Revision Summary

Galvanic Cell converts Chemical → Electrical energy.
EMF E°_cell = E°_cathode − E°_anode.
Nernst Equation: E = E° − (0.059 / n) log Q.
ΔG° = −nFE°_cell = −2.303 RT log K_c.
κ = (1 / R) × (l / A). Λ_m = (κ × 1000) / M.
Λ_m increases with dilution for both strong and weak electrolytes.
Kohlrausch’s Law helps find Λ°_m for weak electrolytes.
Faraday’s Constant (F) ≈ 96500 C mol⁻¹.
Lead-acid battery is a secondary cell (rechargeable).
Cathodic protection is a method to prevent corrosion.

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12
Frequently Asked Questions

What is the function of a salt bridge?

The salt bridge completes the electrical circuit by allowing ions to flow between half-cells and maintains electrical neutrality by preventing the accumulation of charges in the electrolyte solutions.

Why does molar conductivity increase with dilution?

For strong electrolytes, interionic attractions decrease with dilution. For weak electrolytes, the degree of dissociation increases significantly, leading to a higher number of ions in the solution.

Can we store copper sulfate solution in a zinc pot?

No. Zinc is more reactive than copper (has a lower reduction potential). Zinc will displace copper from the solution (Zn + CuSO₄ → ZnSO₄ + Cu), leading to the deterioration of the pot.

What is the difference between a primary and a secondary cell?

In primary cells (like dry cells), the reaction occurs only once and they cannot be recharged. Secondary cells (like lead-acid batteries) can be recharged by passing current in the opposite direction.

Under what condition is E_cell = 0?

E_cell becomes zero when the electrochemical system reaches state of chemical equilibrium. At this point, the reaction quotient (Q) equals the equilibrium constant (K).

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Table of Contents — Chemistry Class 12

Chemistry — Class 12

01	Solutions	Go to page
02	Electrochemistry	Go to page
03	Chemical Kinetics	Go to page
04	d- and f-Block Elements	Go to page
05	Coordination Compounds	Go to page
06	Haloalkanes and Haloarenes	Go to page
07	Alcohols, Phenols and Ethers	Go to page
08	Aldehydes, Ketones and Carboxylic Acids	Go to page
09	Amines	Go to page
10	Biomolecules	Go to page