The Whole Chapter in One Glance

Electrochemistry connects redox reactions with electricity. A galvanic cell turns a spontaneous reaction into current; an electrolytic cell uses current to drive a non-spontaneous one. The Nernst equation links potential to concentration; thermodynamics links it to ΔG\Delta G and KcK_c. Conductance describes how solutions carry current; Kohlrausch's law dissects it ion by ion; Faraday's laws quantify electrolysis; and batteries, fuel cells and corrosion are the real-world payoff.

Electrochemistry chapter overview mind map

Slot every concept and numerical into one of these six branches.

Master Formula Sheet

Cell potential: Ecell∘=Ecathode∘−Eanode∘E^\circ_{cell}=E^\circ_{cathode}-E^\circ_{anode} (reduction potentials). Positive Ecell∘E^\circ_{cell} → spontaneous.

Nernst equation (298 K): Ecell=Ecell∘−0.059nlog⁡QE_{cell}=E^\circ_{cell}-\dfrac{0.059}{n}\log Q

Thermodynamic links:

  • ΔrG∘=−nFEcell∘\Delta_r G^\circ = -nFE^\circ_{cell}
  • Ecell∘=0.059nlog⁡KcE^\circ_{cell}=\dfrac{0.059}{n}\log K_c
  • wmax=nFEcell∘w_{max}=nFE^\circ_{cell}

Conductance:

  • Conductivity κ=1R×lA\kappa=\dfrac{1}{R}\times\dfrac{l}{A}, or κ=G∗ ⁣× ⁣1R\kappa=G^*\!\times\!\dfrac{1}{R} when cell constant G∗=lAG^*=\dfrac{l}{A}
  • Molar conductivity Λm=κ×1000c\Lambda_m=\dfrac{\kappa\times1000}{c} (S cm² mol⁻¹)
  • Kohlrausch: Λm∘=ν+λ+∘+ν−λ−∘\Lambda^\circ_m=\nu_+\lambda^\circ_++\nu_-\lambda^\circ_-
  • Degree of dissociation α=ΛmΛm∘\alpha=\dfrac{\Lambda_m}{\Lambda^\circ_m}; Ka=cα21−αK_a=\dfrac{c\alpha^2}{1-\alpha}

Faraday's laws: m=ZItm=ZIt; moles deposited =ItnF=\dfrac{It}{nF}; 1 F=965001\text{ F}=96500 C mol⁻¹.

Constants: 2.303RTF=0.059\dfrac{2.303RT}{F}=0.059 V at 298 K; ESHE∘=0E^\circ_{SHE}=0.

Quick Comparison Tables

Galvanic vs Electrolytic cell

Feature Galvanic Electrolytic
Energy Chemical → electrical Electrical → chemical
Reaction Spontaneous Non-spontaneous
Anode Negative Positive
Cathode Positive Negative
(Oxidation at anode, reduction at cathode in both)

Strong vs Weak electrolyte (conductivity)

Feature Strong Weak
Dissociation Complete Partial
Λm\Lambda_m vs c\sqrt{c} Straight line Steep curve near c=0
Λm∘\Lambda^\circ_m By extrapolation By Kohlrausch's law

Primary vs Secondary cell

Feature Primary Secondary
Rechargeable No Yes
Examples Dry cell, mercury cell Lead storage, Ni-Cd

Last-Minute Memory Hooks

  • An Ox, Red Cat: Anode = Oxidation, Cathode = Reduction (in both cell types). Only the terminal sign flips between galvanic and electrolytic.
  • Ecell∘=Ecathode∘−Eanode∘E^\circ_{cell}=E^\circ_{cathode}-E^\circ_{anode}; positive → spontaneous → ΔG<0\Delta G<0 → Kc>1K_c>1.
  • Nernst: more product / less reactant lowers EcellE_{cell}. Dead cell: Ecell=0E_{cell}=0, Q=KcQ=K_c.
  • 0.059 is the magic number at 298 K — appears in Nernst and in E∘=0.059nlog⁡KcE^\circ=\frac{0.059}{n}\log K_c.
  • On dilution: κ\kappa down, Λm\Lambda_m up (opposite directions).
  • Kohlrausch combo for acetic acid: CH₃COONa + HCl − NaCl.
  • Faraday recipe: Q=It→Q=It \to mol e⁻ =Q/96500→=Q/96500 \to mol product ÷n→\div n \to mass.
  • Mercury cell = constant voltage (no ionic concentration change). Lead battery acid dilutes on discharge.
  • Rusting needs water + O₂; protect with Zn/Mg (more reactive, sacrificial).

One-line revision flow: Galvanic cell → electrode potential & SHE → Nernst → ΔG & Kc → conductance & Kohlrausch → electrolysis & Faraday → batteries, fuel cells, corrosion.