Maharashtra State Board · Class 12 · Chemistry · Chapter 5

Electrochemistry — Formula Sheet

Board Formulas

12 formulas

1.Cell EMF from Electrode Potentials★
$E_{ce l l}^{\circ} = E_{c a t h o d e}^{\circ} - E_{an o d e}^{\circ}$
Use standard reduction potentials for both. Cell is spontaneous if E°_cell > 0.
2.Gibbs Energy — EMF Relation★
$Δ G^{\circ} = - n F E_{ce l l}^{\circ}$
Links thermodynamics to electrochemistry. n = number of moles of electrons, F = 96500 C/mol.
3.Nernst Equation (electrode)★
$E = E^{\circ} - \frac{0.0591}{n} lo g \frac{[ oxidised ]}{[ reduced ]} (T = 298 K)$
Applies to a single half-cell. In Balbharati form base 10 log with prefactor 0.0591/n V.
4.Nernst Equation (cell)★
$E_{ce l l} = E_{ce l l}^{\circ} - \frac{0.0591}{n} lo g Q Q = reaction quotient$
For general cell reaction. At equilibrium E_cell = 0 and Q = K.
5.Equilibrium Constant from E°
$lo g K = \frac{n E _{ce l l}^{\circ}}{0.0591}$
Larger E° ⇒ larger K ⇒ more spontaneous reaction.
6.Faraday's First Law
$w = Z I t$
Mass deposited proportional to charge passed. Z = electrochemical equivalent (kg/C).
7.Faraday's Second Law
$\frac{w _{1}}{w _{2}} = \frac{E _{1}}{E _{2}}$
For same charge, masses deposited proportional to equivalent weights.
8.Conductivity and Molar Conductivity
$κ = \frac{1}{ρ}, Λ_{m} = \frac{κ \times 1000}{c}$
$κ$ : Specific conductivity (S/m) · $Λ_{m}$ : Molar conductivity (S·cm²·mol⁻¹) · $c$ : Concentration (mol/L)
κ in S·cm⁻¹ (or S·m⁻¹). Λ_m in S·cm²·mol⁻¹ if c in mol/L, κ in S/cm.
9.Kohlrausch's Law★
$Λ_{m}^{\infty} = λ_{+}^{\infty} + λ_{-}^{\infty}$
At infinite dilution, the limiting molar conductivity is the sum of ionic contributions.
10.Degree of Dissociation from Λ
$α = \frac{Λ _{m}}{Λ _{m}^{\infty}}$
Fraction of molecules dissociated; ratio of measured to infinite-dilution molar conductivity.
11.Ostwald's Dilution Law
$K_{a} = \frac{c α ^{2}}{1 - α}$
For a weak monobasic acid HA. When α ≪ 1, K_a ≈ cα² ⇒ α = √(K_a/c).
12.Cell Constant
$G^{*} = \frac{l}{A} = κ \cdot R$
Only geometric; unit cm⁻¹ or m⁻¹.