Electrochemistry - COMPLETE EXAM Quick Revision NOTES with full formula sheet{Part1}

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ELECTROCHEMISTRY, COMPLETE EXAM NOTES

This is to the point quick last minutes revision notes

 Introduction to Electrochemistry

Definition: Branch of physical chemistry that studies interconversion of chemical energy and electrical energy.

Two Main Processes:

  • Spontaneous chemical reactions → electricity (Galvanic/Voltaic cell)
  • Electricity → chemical reactions (Electrolytic cell)

Electricity: Flow of electrons between two points.



Redox Reactions

Redox Reaction: Oxidation and reduction occur simultaneously.

Oxidation:

  • Loss of electrons
  • Gain of oxygen
  • Loss of hydrogen
  • Increase in oxidation state

Reduction:

  • Gain of electrons
  • Loss of oxygen
  • Gain of hydrogen
  • Decrease in oxidation state

Disproportionation Reaction: Same species oxidized and reduced in same reaction.

 Oxidation State vs Valency

Oxidation State: Apparent charge on atom in compound.

Valency: Combining capacity, no sign.

 Rules for Oxidation State

  • Free elements = 0
  • H = +1 (non-metals), -1 (metal hydrides)
  • O = -2 (exceptions: peroxides -1, superoxides -1/2, OF₂ +2)
  • Group 1 = +1
  • Group 2 = +2
  • Fluorine = -1 always

 Electrochemical Cells

Feature Electrolytic Cell Galvanic Cell
Energy Electrical → Chemical Chemical → Electrical
Reaction Non-spontaneous Spontaneous
Anode Positive Negative
Cathode Negative Positive

 Salt Bridge

U-shaped tube filled with inert electrolyte (KCl/KNO₃ in agar-agar).

Functions:
  • Completes circuit
  • Maintains electrical neutrality
  • Prevents mixing of solutions

 Faraday’s Laws of Electrolysis

First Law:

Mass deposited ∝ charge passed

w = ZIt

Second Law:

For same electricity, mass ∝ equivalent weight

Faraday Constant: 96500 C/mol


 Conductance & Conductivity

Electrolytic conduction: Due to ions, increases with temperature

Metallic conduction: Due to electrons, decreases with temperature

Conductance: G = 1/R

Molar Conductivity: Conductance of ions from 1 mole electrolyte

Trend: Increases with dilution (VERY IMPORTANT)

 Electrochemical Series

Arrangement of elements based on standard reduction potentials.

Standard Hydrogen Electrode (SHE): 0.00 V reference

Applications:

  • Predict reactivity
  • Displacement reactions
  • Check spontaneity of reaction

Rule: Ecell > 0 → spontaneous reaction

 Electrode Potential & EMF

Electrode Potential: Tendency to lose/gain electrons

Cell EMF:

Ecell = Ecathode - Eanode

Nernst Equation

VERY IMPORTANT FOR EXAMS

E = E° − (0.0591/n) log Q

Used for:

  • Non-standard conditions
  • Concentration cells
  • EMF calculations

Read Other


Kohlrausch’s Law

At infinite dilution:

Λm° = λ⁺ + λ⁻

Used for:

  • Weak electrolyte conductivity
  • Degree of dissociation

 Batteries & Fuel Cells

  • Primary Cells: Non-rechargeable (Dry cell, Mercury cell)
  • Secondary Cells: Rechargeable (Lead storage battery, Ni-Cd)
  • Fuel Cells: H₂ + O₂ → electricity + water

Corrosion

Definition: Slow destruction of metals due to environment

Rusting of Iron: Fe₂O₃·xH₂O formation

Mechanism:

  • Anode: Fe → Fe²⁺ + 2e⁻
  • Cathode: O₂ + H₂O + e⁻ → OH⁻

Prevention:

  • Painting
  • Galvanization
  • Cathodic protection (Mg/Zn)

Electrolysis of Water

  • Cathode: H₂ gas
  • Anode: O₂ gas

 HIGH-YIELD POINTS

  • Faraday laws numericals
  • Nernst equation derivations & applications
  • Cell notation representation
  • EMF calculations
  • Electrochemical series order
  • Corrosion mechanism reactions
  • Conductivity vs temperature trends

Electrochemistry, Formula Sheet

More to come, Comment to get Pdf Of full formula sheet for quick revisions
Topic Formula Notes
Electric Charge Q = I × t Charge (Coulombs)
Faraday First Law w = ZIt Mass deposited ∝ charge
Faraday General Formula w = (It × M) / (nF) M = molar mass
Moles of Electrons n (moles) = Q / F = It / F Used in numericals
Faraday Constant F = 96485 C/mol Standard accurate value
Cell EMF Ecell = Ecathode − Eanode Spontaneous if positive
Standard EMF E°cell = E°cathode − E°anode Standard conditions
Nernst Equation (General) E = E° − (RT/nF) ln Q Valid at all temperatures
Nernst Equation (25°C) E = E° − (0.0592/n) log Q At 298 K
Equilibrium Relation E°cell = (0.0592/n) log K At equilibrium
At Equilibrium Ecell = 0 and Q = K No net reaction
Gibbs Free Energy ΔG = −nFEcell Work relation
Standard Gibbs Energy ΔG° = −nFE°cell Standard condition
Resistance R = V / I Ohm’s law
Resistance Relation R = ρ (L / A) L = length, A = area
Resistivity ρ = R (A / L) Correct rearranged form
Conductance G = 1 / R Unit: Siemens
Conductivity κ = 1 / ρ Also κ = G × (L/A)
Cell Constant Cell constant = L / A Geometry factor
Molar Conductivity Λm = κ × (1000 / C) C in mol/L
Equivalent Conductivity Λeq = κ × (1000 / N) N = normality
Kohlrausch Law Λm° = λ⁺ + λ⁻ At infinite dilution
Degree of Dissociation α = Λm / Λm° Weak electrolytes
Ostwald Dilution Law K = (Cα²) / (1 − α) Weak electrolytes
Ostwald Approximation K ≈ Cα² (if α ≪ 1) MCQ shortcut
Concentration Cell Ecell = (0.0592/n) log (C₂ / C₁) C₂ > C₁
Overpotential η = Eapplied − Eequilibrium Extra voltage required

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