Electrochemistry

part 1

Electrochemical Cells

• Electrochemical cells — galvanic and electrolytic
• Galvanic cells — Daniel cell
• Electrode potential and standard electrode potential
• Electrochemical series

part 2

Nernst Equation and Gibbs Energy

• Nernst equation
• EMF of a cell using Nernst equation
• Equilibrium constant from EMF
• Gibbs energy and cell potential
• Fuel cells

part 3

Conductance and Electrolysis

• Conductance in electrolytic solutions
• Molar conductivity — variation with concentration
• Kohlrausch's law
• Electrolysis — Faraday's laws
• Corrosion and its prevention

Standard cell potential

$E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$

★ board favourite

Nernst equation

$E_{cell} = E^\circ_{cell} - \frac{0.0592}{n}\log Q$ (at 25°C)

★ board favourite

Gibbs energy and cell potential

$\Delta G^\circ = -nFE^\circ_{cell}$

★ board favourite

Equilibrium constant from E°

$\log K = \frac{nE^\circ_{cell}}{0.0592}$

★ board favourite

Faraday's first law of electrolysis

$m = ZIt = \frac{M}{nF} \cdot It$

★ board favourite

Kohlrausch's law (strong electrolyte)

$\Lambda_m = \Lambda^\circ_m - b\sqrt{c}$

★ frequently asked

Molar conductivity at infinite dilution

$\Lambda^\circ_m = \nu_+\lambda^\circ_+ + \nu_-\lambda^\circ_-$

★ frequently asked

Degree of dissociation from conductivity

$\alpha = \frac{\Lambda_m}{\Lambda^\circ_m}$

★ frequently asked

Faraday's second law

$\frac{m_1}{m_2} = \frac{E_1}{E_2}$ (E = equivalent weight)

★ frequently asked

Calculate the EMF of the cell at 298 K: Mg(s)|Mg²⁺(0.1M)||Ag⁺(1×10⁻³M)|Ag(s). Given E°(Mg²⁺/Mg) = −2.37 V and E°(Ag⁺/Ag) = +0.80 V.

State Kohlrausch's law of independent migration of ions. How is it used to calculate the molar conductivity of a weak electrolyte at infinite dilution?

Write the Nernst equation for an electrochemical cell. Calculate the EMF of the cell: Zn|Zn²⁺(0.1M)||Cu²⁺(0.01M)|Cu, given E°cell = 1.10V at 298K.

(a) Draw a labelled diagram of a standard hydrogen electrode. (b) Write the relationship between standard cell potential and Gibbs energy of a cell reaction. (c) Calculate ΔG° for a cell with E°cell = 1.10 V (n = 2, F = 96500 C/mol).

State Faraday's laws of electrolysis. How many grams of copper will be deposited when a current of 2A is passed through CuSO₄ solution for 30 minutes? (Atomic mass of Cu = 63.5, Faraday's constant = 96500 C/mol)

Define conductivity and molar conductivity of a solution. State how each of them changes with (i) increase in concentration and (ii) dilution. Give the SI unit of molar conductivity.

What is molar conductivity? How does it vary with dilution for (a) strong electrolytes, (b) weak electrolytes?

Write the Nernst equation and calculate the cell potential for: Ni(s)|Ni²⁺(0.01M)||Cu²⁺(0.1M)|Cu(s). Given E°cell = 0.59 V at 298 K.

A solution of AgNO₃ is electrolysed for a certain time with a current of 1.5 A and 1.078 g of silver is deposited. Calculate the time for which the current was passed. (Atomic mass of Ag = 108)

(i) Why does the cell potential of a mercury cell remain constant during its life? (ii) Write the electrode reactions occurring in a lead storage battery during discharge.

Why is it that the standard electrode potential of the hydrogen electrode is taken as zero?

How many marks is Electrochemistry worth in the Class 12 board exam?

Around 9 marks of the 70-mark CBSE Chemistry theory paper, based on the official unit-wise weightage. Nernst equation numerics and Faraday's laws — practise daily.

Is Electrochemistry easy or hard?

It's rated hard — one of the tougher chapters in Class 12 Chemistry. Most students need about 5 hours to cover it well.

What are the important topics in Electrochemistry?

The chapter covers 12 NCERT topics in 3 areas: Electrochemical Cells; Nernst Equation and Gibbs Energy; Conductance and Electrolysis.

What questions come from Electrochemistry in board exams?

Between 2018–2024, CBSE board papers asked questions from this chapter on Nernst Equation, Kohlrausch's Law, Electrochemical Cells, Faraday's Laws — 1- to 5-mark questions.