Electrochemistry: Galvanic Cells, Nernst Equation, Conductance and Electrolysis for NEET by Physics Wallah

Electrochemistry mixes ideas from chemistry and physics, and many NEET students do not know where to begin. Cell diagrams, electrode potentials, the Nernst equation, conductance and electrolysis each follow their own rules. One wrong sign or one wrong electrode can change the whole answer.

Below details follow the order of the lecture, from the Daniel cell to batteries and galvanisation, and end with six practice questions. Each part is short and easy to scan, so revision is quicker. PW’s online Chemistry classes can help you practise the same chapter with notes and tests.

What Is Electrochemistry?

Electrochemistry is the study of how chemical energy and electrical energy change into each other. Every topic in the chapter builds on this one idea.

The lecture also gives a study tip. Students should ignore rumours and worries about next year’s exam rules, and focus on revision and practice instead.

Galvanic Cell and Salt Bridge

A galvanic cell is explained using the Daniel cell. It has two electrodes, and each one does a different job.

• Zinc (anode): The zinc electrode dissolves.

• Copper (cathode): Copper deposits on the copper electrode.

• Electron flow: Electrons move from the anode to the cathode.

• Salt bridge: It keeps the solutions electrically neutral and completes the circuit.

Electrode Potential and Electrochemical Series

Electrode potential tells you how strongly an electrode tends to change. There are two kinds, and each shows a different tendency.

• Oxidation potential: It shows the tendency to be oxidised.

• Reduction potential: It shows the tendency to be reduced.

Using these values, you can find the oxidising and reducing power of a substance. You can also decide which electrode is the anode and which is the cathode in a cell, and which reaction is spontaneous.

Nernst Equation and Cell EMF

Students often mix up standard EMF and actual EMF. The table below compares what each one depends on. Learn this difference well, because direct questions are asked on it.

The Nernst equation is used to find the actual cell EMF. The lecture also uses it to show how cell EMF is related to free energy.

Reference Electrode and Concentration Cells

Electrode potentials need a starting point. The standard hydrogen electrode is taken as the reference, and other potentials are found against it.

• Adding EMF values: Do not add EMF values directly. Apply the conservation of free energy instead.

• Concentration cell: The standard EMF is zero. The actual EMF still arises because of the difference in concentration.

Conductance and Molar Conductivity

The lecture first practises cell EMF questions on the Nernst equation, oxidation and reduction potential, equilibrium constant and free energy. It then moves to conductance.

• Types of conductance: Metallic and ionic conductance are compared, along with the effect of temperature on each.

• Formulas and units: Learn them for resistance, conductance, specific conductance and molar or equivalent conductance.

• Effect of dilution: Conductance goes down on dilution. Molar conductivity goes up and reaches a limiting value.

• Kohlrausch’s law: It is used to find this limiting value.

Uses of Conductivity

Conductivity is not only a definition topic. The lecture shows how it is used in calculations through examples.

• Degree of dissociation: Found from conductivity.

• Ionization constant: Found from conductivity.

• pH: Found from conductivity.

Question 6 below uses this idea.

Faraday’s Laws and Electrolysis Products

Faraday’s laws connect the charge passed with the mass deposited. For the same charge, the mass deposited is in the ratio of the equivalent masses.

Deciding the products of electrolysis is a scoring topic. The table below lists what to check at each electrode. Go through these points one by one in every question.

Batteries, Corrosion and Final Practice

The lecture ends with mixed practice. It covers calculations based on Faraday’s laws, products from aqueous and molten salts, and questions on batteries and galvanisation.

1. Terminal Potential Difference of a Non-Ideal Battery

For a battery with EMF E and internal resistance r:

2. Series Combination of Cells

• n identical cells (E, r) in series: E_eq = nE, r_eq = nr.

• n identical cells (E, r), m reversed polarity: E_eq = (n - 2m)E, r_eq = nr.

3. Parallel Combination of Cells

• m identical cells (E, r) in parallel: E_eq = E, r_eq = r/m.

• Non-identical cells: E_eq = (E1/r1 + E2/r2 + …) / (1/r1 + 1/r2 + …), 1/r_eq = 1/r1 + 1/r2 + …

Important Electrochemistry Questions for NEET

These questions appear in the lecture. Try each one yourself before you look for a solution.

Question 1

Select the correct cell reaction of the cell Pt(s)|Cl₂(g)|Cl⁻(aq)||Ag⁺(aq)|Ag(s):

1. Cl₂(g) + Ag⁺(aq) → Ag(s) + 2Cl⁻(aq)

2. Cl₂(g) + Ag(s) → 2Cl⁻(aq) + 2Ag⁺(aq)

3. 2Cl⁻(aq) + 2Ag⁺(aq) → 2Ag(s) + Cl₂(g)

4. AgCl(s) → Ag⁺(aq) + Cl⁻(aq)

Question 2

Match List-I with List-II.

1. (A)-(IV), (B)-(I), (C)-(II), (D)-(III)

2. (A)-(IV), (B)-(I), (C)-(III), (D)-(II)

3. (A)-(I), (B)-(IV), (C)-(II), (D)-(III)

4. [Option 4 is cut off in the screenshot. Add it from the video.]

Question 3

The standard electrode potential E°(I₂/I⁻), E°(Br⁻/Br₂) and E°(Fe/Fe²⁺) are respectively +0.54 V, −1.09 V and 0.44 V. On the basis of above data which of the following process is non-spontaneous

1. Br₂ + 2I⁻ → 2Br⁻ + I₂

2. Fe + Br₂ → Fe²⁺ + 2Br⁻

3. Fe + I₂ → Fe²⁺ + 2I⁻

4. I₂ + 2Br⁻ → 2I⁻ + Br₂

Question 4

In the electrochemical reaction 2Fe⁺³ + Zn → Zn⁺² + 2Fe⁺² increasing the concentration of Fe⁺²:

1. Increase the cell EMF

2. Increase the current flow

3. Decrease the cell EMF

4. Alter the pH of the solution

Question 5

Find ΔG° of the reaction 2 A(s) + 3 B⁺²(aq) → 2 A⁺³(aq) + 3 B(s) When [B⁺²] = [A⁺²] = 1M.
Given: E°(A⁺³/A) = 0.34 V and E°(B⁺²/B) = −0.16 V

1. 0

2. 96.5 kJ

3. 570 kJ

4. 289.5 kJ

Question 6

Equivalent conductance of 0.1 M solution of HA (weak acid) is 10 S cm² equivalent⁻¹ and at infinite dilution is 200 S cm² equivalent⁻¹. Hence pH of HA solution is

1. 1.3

2. 1.7

3. 2.3

4. 3.7

Exam Tips and Common Mistakes to Avoid 

Review these exam tips and common mistakes to strengthen your understanding of Electrochemistry and avoid errors in numerical and conceptual questions. 

• Question trend: The questions above test cell reactions from cell notation, electrode terms, spontaneity from electrode potentials, the effect of concentration on EMF, ΔG° from E° values and pH from conductance.

• Standard EMF: It does not change with stoichiometric coefficients, electrode thickness or concentration. Actual EMF does change with temperature, pressure and concentration.

• Combining potentials: Do not add EMF values directly. Use the conservation of free energy.

• Concentration cells: Standard EMF is zero, but the actual EMF is not zero when the concentrations differ.

• Anode and cathode: Decide them from the oxidation and reduction potentials before writing the cell reaction.

• Electrolysis products: Always check the electrode type, the medium and the priority of ions.

• Preparation: Read the NCERT material on batteries and finish the homework given in the lecture. Focus on revision and practice.

Revise electrode potentials, practise cell EMF calculations and understand how concentration affects electrochemical reactions. Working through previous year questions and reviewing common mistakes can help you improve accuracy and approach Electrochemistry questions with greater confidence in your NEET preparation. For regular practice with live classes and tests, you can explore PW NEET online coaching.

Related Resources

• NEET Physics syllabus

• Class 12 Physics notes

• Chemistry Electrochemistry NEET PYQ

• NEET Physics important chapters

• NEET previous year question papers