Lesson Plan: Electrochemistry (Class 12)

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Physical Chemistry (Class 12)

Electrochemistry

The bridge between chemical energy and electrical energy. This chapter builds directly on Redox Reactions. The core challenge is mastering the Nernst Equation calculations and understanding the difference between Galvanic and Electrolytic cells.

⚡

⚠️ Prerequisites

• Redox Reactions: Identifying Anode (Oxidation) and Cathode (Reduction).
• Equilibrium: Calculation of Reaction Quotient ($Q$).
• Thermodynamics: Relationship between $\Delta G$ and work.

🧠 Study Approach

Sign Convention is King: Remember LOAN (Left Oxidation Anode Negative) for Galvanic cells. For calculations, unit conversion in Conductivity ($\kappa$) is the most common trap.

Study Sequence

1. Galvanic Cells (Daniell Cell)

Construction & Working. Function of Salt Bridge.
Electrode Potential ($E^\circ$): Standard Hydrogen Electrode (SHE). Electrochemical Series.

2. Nernst Equation (CRITICAL)

Calculating EMF at non-standard conditions.
$E_{cell} = E^\circ_{cell} - \frac{0.059}{n} \log Q$.
Calculation of Equilibrium Constant ($K_c$) from $E^\circ_{cell}$.

3. Thermodynamics of Cell

Relationship between Gibbs Energy and Cell Potential: $\Delta G^\circ = -nFE^\circ_{cell}$.
Criteria for spontaneity ($\Delta G < 0 \implies E_{cell} > 0$).

4. Conductance of Electrolytic Solutions

Resistance ($R$), Conductance ($G$), Conductivity ($\kappa$), and Molar Conductivity ($\Lambda_m$).
Variation of $\kappa$ and $\Lambda_m$ with concentration (Strong vs Weak electrolytes).

5. Kohlrausch Law

Limiting Molar Conductivity ($\Lambda_m^\circ$). Calculation of $\Lambda_m^\circ$ for weak electrolytes. Determination of Degree of Dissociation ($\alpha = \Lambda_m / \Lambda_m^\circ$).

6. Electrolysis & Faraday's Laws

First Law: $W = ZIt$. Second Law: Equivalents Ratio.
Predicting products of electrolysis (Preferential Discharge Theory: e.g., Aqueous NaCl vs Molten NaCl).

7. Batteries & Corrosion

Primary (Dry Cell, Mercury) vs Secondary Cells (Lead Storage, Ni-Cd).
Fuel Cells: $H_2-O_2$ cell efficiency.
Corrosion: Electrochemical theory of rusting and prevention (Sacrificial protection).

🎯 How to Practice

1

Nernst Log Logic: Practice converting $Q$ to powers of 10.
e.g., $\log(2 \times 10^{-3}) = \log 2 - 3 \log 10 = 0.3 - 3 = -2.7$.

2

Product Prediction: Memorize the discharge potential order. Know why $Cl_2$ is produced instead of $O_2$ in aqueous NaCl electrolysis (Overpotential of Oxygen).

3

Unit Trap: In $\Lambda_m = \frac{\kappa \times 1000}{M}$, if $\kappa$ is in $S/cm$, then $\Lambda_m$ is in $S \ cm^2 \ mol^{-1}$. If $\kappa$ is in $S/m$, the formula changes! Stick to $cm$ units to avoid confusion.

📝 Quick Revision Formulas

Nernst Equation (at 298K) $$E_{cell} = E^\circ_{cell} - \frac{0.059}{n} \log \frac{[\text{Prod}]}{[\text{React}]}$$

Thermodynamics $$\Delta G^\circ = -n F E^\circ_{cell}$$ $$\log K_c = \frac{n E^\circ_{cell}}{0.059}$$

Conductivity $$G = \frac{1}{R} = \frac{\kappa A}{l}$$ $$\Lambda_m = \frac{\kappa \times 1000}{M}$$

Faraday's Law $$W = Z I t$$ $$W = \frac{\text{Atomic Mass}}{n \times 96500} \times I \times t$$

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