NCERT Solutions for Class 12 Chemistry Chapter 2 Electrochemistry

Short Note:

• Galvanic Cell (Voltaic Cell): Device converting chemical energy stored in a spontaneous redox reaction into electrical energy (e.g., Daniell Cell: $\text{Zn(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Zn}^{2+}\text{(aq)} + \text{Cu(s)}$).

• Standard Cell Potential ($E^\circ_{\text{cell}}$): $E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}$ (measured against Standard Hydrogen Electrode, $E^\circ = 0\text{ V}$).

• Nernst Equation (at 298 K): Relates cell potential to ion concentration:

  $E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{0.0591}{n} \log \frac{[\text{Products}]}{[\text{Reactants}]}$

• Equilibrium Constant ($K_c$) & Gibbs Free Energy ($\Delta G^\circ$):

  - $\log K_c = \frac{n \cdot E^\circ_{\text{cell}}}{0.0591}$

  - $\Delta G^\circ = -n F E^\circ_{\text{cell}}$ (where $F = 96487\text{ C mol}^{-1} \approx 96500\text{ C mol}^{-1}$)

Short Note:

• Conductivity ($\kappa$): Inverse of resistivity ($\kappa = 1/\rho = \frac{1}{R} \cdot \frac{l}{A}$). Unit: $\text{S m}^{-1}$ or $\text{S cm}^{-1}$.

• Molar Conductivity ($\Lambda_m$): Conductance of a solution containing $1\text{ mole}$ of electrolyte:

  $\Lambda_m = \frac{\kappa \times 1000}{M}$ (where $M$ is molarity in $\text{mol L}^{-1}$). Unit: $\text{S cm}^2 \text{mol}^{-1}$.

• Variation with Dilution:

  - $\kappa$ decreases with dilution because number of ions per unit volume decreases.

  - $\Lambda_m$ increases with dilution for both strong and weak electrolytes.

• Kohlrausch's Law of Independent Migration of Ions: At infinite dilution, molar conductivity of an electrolyte is equal to the sum of ionic conductivities of its constituent cations and anions:

  $\Lambda_m^\circ = \nu_+ \lambda_+^\circ + \nu_- \lambda_-^\circ$

• Degree of Dissociation ($\alpha$) for Weak Electrolyte: $\alpha = \frac{\Lambda_m}{\Lambda_m^\circ}$

Short Note:

• Faraday's Laws of Electrolysis:

  - 1st Law: Mass deposited $m = Z \cdot Q = Z \cdot I \cdot t$ (where $Z$ is electrochemical equivalent).

  - 2nd Law: For same quantity of electricity, masses deposited are proportional to equivalent weights ($m_1 / m_2 = E_1 / E_2$).

• Commercial Batteries:

  - Primary Batteries: Cannot be recharged (e.g., Dry Cell, Mercury Cell).

  - Secondary Batteries: Rechargeable (e.g., Lead storage battery, Ni-Cd cell).

• Fuel Cells: Devices converting energy from combustion of fuels (like $\text{H}_2, \text{CH}_4$) directly into electrical energy (e.g., $\text{H}_2-\text{O}_2$ fuel cell with ~70% efficiency).

• Corrosion: Electrochemical phenomenon where metal gets oxidized. Anodic region: $\text{Fe(s)} \rightarrow \text{Fe}^{2+} + 2e^-$; Cathodic region: $\text{O}_2 + 4\text{H}^+ + 4e^- \rightarrow 2\text{H}_2\text{O}$. Prevents by sacrificial coating (Galvanization using Zinc).