Jeemate
ChemistryPhysical ChemistryTop Priority (3-4 Qs in JEE)

Electrochemistry & Conductance Formulas

Nernst equation, Gibbs energy of cell, Kohlrausch law, Faraday laws of electrolysis, and molar conductivity.

8 Formulas•685+ Questions in Bank

Concept Diagram

Daniell Electrochemical Cell
Zn Anode (-)1M ZnSO₄ (aq)Cu Cathode (+)1M CuSO₄ (aq)Salt Bridge (KCl)1.1Ve⁻ flowZn + Cu²⁺ → Zn²⁺ + Cu (E°cell = 1.10 V)
Zn(s)|Zn²⁺(aq) || Cu²⁺(aq)|Cu(s) galvanic cell with salt bridge, electron flow from anode to cathode, and standard EMF of 1.10 V.

Core Formulas & Mathematical Identities

8
01

Nernst Equation (at 298 K)

Ecell=Ecell∘−0.0591nlog⁡10QE_{\text{cell}} = E^\circ_{\text{cell}} - \frac{0.0591}{n} \log_{10} Q

Computes non-standard cell potential under varying ion concentrations.

Examiner Tip: At equilibrium, E_cell = 0 and Q = K_eq.
02

Standard Cell Potential & Free Energy

ΔG∘=−nFEcell∘,log⁡10K=nEcell∘0.0591\Delta G^\circ = -n F E^\circ_{\text{cell}}, \quad \log_{10} K = \frac{n E^\circ_{\text{cell}}}{0.0591}

Connects electrochemical cell voltage to standard Gibbs energy and equilibrium constant.

Examiner Tip: F = Faraday constant ≈ 96500 C/mol.
03

Molar Conductivity & Kohlrausch's Law

Λm=κ×1000M  (S cm2mol−1),Λm∘=ν+λ+∘+ν−λ−∘\Lambda_m = \frac{\kappa \times 1000}{M} \; (\text{S cm}^2\text{mol}^{-1}), \quad \Lambda_m^\circ = \nu_+ \lambda_+^\circ + \nu_- \lambda_-^\circ

Independent migration of ions at infinite dilution.

Examiner Tip: Degree of dissociation of weak electrolyte: α = Λ_m / Λ_m°.
04

Faraday's Laws of Electrolysis

w=ZIt=(E96500)It,w1E1=w2E2w = Z I t = \left(\frac{E}{96500}\right) I t, \quad \frac{w_1}{E_1} = \frac{w_2}{E_2}

Mass w of substance liberated at electrode by current I in time t.

Examiner Tip: Equivalent weight E = Molar mass / n-factor.
05

Concentration Cell EMF

Ecell=0.0591nlog⁡10C2C1(C2>C1)E_{\text{cell}} = \frac{0.0591}{n} \log_{10}\frac{C_2}{C_1} \quad (C_2 > C_1)

EMF generated purely by concentration difference of identical electrodes.

Examiner Tip: E°_cell is identically ZERO for concentration cells.
06

Debye-Hückel-Onsager Equation (Strong Electrolytes)

Λm=Λm∘−AC\Lambda_m = \Lambda_m^\circ - A\sqrt{C}

Linear variation of molar conductance with square root of concentration for completely dissociated strong electrolytes.

Examiner Tip: Extrapolation to C → 0 gives limiting molar conductance Λ_m° for strong electrolytes (cannot be extrapolated for weak electrolytes).
07

Solubility of Sparingly Soluble Salts via Conductance

S=κ×1000Λm∘  (mol/L),Ksp=[Mz+]x[Xz−]yS = \frac{\kappa \times 1000}{\Lambda_m^\circ} \; (\text{mol/L}), \quad K_{sp} = [M^{z+}]^x [X^{z-}]^y

Determining microscopic solubility S and solubility product K_sp from electrolytic specific conductance κ.

Examiner Tip: Specific conductance of salt alone is κ_salt = κ_solution - κ_water.
08

Cell Thermodynamics & Fuel Cell Efficiency

ΔS=nF(∂E∂T)P,ΔH=−nFE+nFT(∂E∂T)P,ηfuel cell=ΔG∘ΔH∘\Delta S = n F \left(\frac{\partial E}{\partial T}\right)_P, \quad \Delta H = -nFE + nFT\left(\frac{\partial E}{\partial T}\right)_P, \quad \eta_{\text{fuel cell}} = \frac{\Delta G^\circ}{\Delta H^\circ}

Entropy, enthalpy of cell reaction derived from temperature coefficient (∂E/∂T)_P, and theoretical efficiency of H₂-O₂ fuel cells.

Examiner Tip: If (∂E/∂T)_P > 0, cell absorbs heat from surroundings during operation and ΔS > 0.

Top Examiner Traps & Pitfalls

Frequently tested misconceptions in Electrochemistry & Conductance

  • •Nernst equation at 298 K uses 0.0591/n with log base 10, NOT natural log ln.
  • •E°_cell is an INTENSIVE property and does not change when multiplying chemical equation coefficients, but ΔG° is EXTENSIVE.
Previous Chapter

Chemical & Ionic Equilibrium

8 Formulas•Physical Chemistry
Next Chapter

Solutions & Colligative Properties

Physical Chemistry•8 Formulas