CBSE · Class 12 · Chemistry · Chapter 2

Electrochemistry — Formula Sheet

Board Formulas

10 formulas

1.Standard EMF of Cell★
$E_{ce l l}^{\circ} = E_{c a t h o d e}^{\circ} - E_{an o d e}^{\circ}$
$E_{ce l l}^{\circ}$ : Standard cell potential (V) · $E_{c a t h o d e}^{\circ}$ : SRP of the cathode (reduction site) · $E_{an o d e}^{\circ}$ : SRP of the anode (oxidation site)
Both electrode potentials as reduction potentials (SRP). Positive E°(cell) ⇒ spontaneous reaction.
2.Nernst Equation (general)★
$E_{ce l l} = E_{ce l l}^{\circ} - \frac{R T}{n F} ln Q$
Gives cell potential at non-standard concentrations. Q is reaction quotient.
3.Nernst Equation at 298 K★
$E_{ce l l} = E_{ce l l}^{\circ} - \frac{0.0591}{n} lo g Q$
Numerical version. Learn this 298 K form for quick calculation. n = number of electrons transferred.
4.Gibbs Free Energy and EMF★
$Δ G^{\circ} = - n F E_{ce l l}^{\circ} = - R T ln K_{c}$
$n$ : Moles of electrons transferred · $F$ : Faraday's constant = 96500 C/mol · $K_{c}$ : Equilibrium constant of cell reaction
Links thermodynamics with electrochemistry. F = 96500 C/mol. Also gives equilibrium constant K_c of cell reaction.
5.Conductance & Specific Conductivity
$κ = \frac{1}{ρ} = G \times \frac{l}{A}$
$κ$ : Specific conductivity (S·cm⁻¹) · $G$ : Conductance = 1/R (siemens, S) · $l / A$ : Cell constant (cm⁻¹)
κ = specific conductivity (S/cm). G = conductance (S). l/A = cell constant (cm⁻¹). ρ = resistivity.
6.Molar Conductivity★
$Λ_{m} = \frac{κ \times 1000}{c}$
$Λ_{m}$ : Molar conductivity (S·cm²·mol⁻¹) · $c$ : Molar concentration (mol/L)
c = molarity (mol/L). Units of Λm: S·cm²·mol⁻¹. Increases as dilution increases (fewer inter-ionic interactions).
7.Kohlrausch's Law of Independent Migration★
$Λ_{m}^{\circ} = ν_{+} λ_{+}^{\circ} + ν_{-} λ_{-}^{\circ}$
Limiting molar conductivity = sum of contributions from cation and anion. Used to find Λ°m of weak electrolytes indirectly.
8.Degree of Dissociation (weak electrolyte)
$α = \frac{Λ _{m}^{c}}{Λ _{m}^{\circ}}, K_{a} = \frac{c α ^{2}}{1 - α}$
Λ_m at concentration c divided by limiting Λ°m. Substitute into Ostwald's dilution law to find K_a.
9.Faraday's First Law of Electrolysis★
$w = Z \cdot Q = Z \cdot I \cdot t = \frac{E \cdot I \cdot t}{F}$
$w$ : Mass deposited (g) · $E$ : Equivalent mass = molar mass / n · $I$ : Current (A) · $t$ : Time (s) · $F$ : Faraday = 96500 C/mol
Mass deposited (w) ∝ charge (Q). Z = electrochemical equivalent. E = M/n (equivalent mass).
10.Faraday's Second Law
$\frac{w _{1}}{w _{2}} = \frac{E _{1}}{E _{2}}$
Same quantity of charge through different electrolytes ⇒ masses deposited are in the ratio of their equivalent masses.