1.10V
Zn²⁺
SO₄²⁻
Electrochemical Cells
World B — Acids, Bases & Solutions
22.A — CELL TYPES & COMPONENTS
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R22.01 Galvanic (Voltaic) Cells
- Chemical energy → Electrical energy.
- Spontaneous redox reaction ($\Delta G < 0$).
- Requires two separate half-cells.
BAT
R22.02 Electrolytic Cells
- Electrical energy → Chemical energy.
- Non-spontaneous reaction forced by external voltage.
- Typically in a single container.
K⁺
Cl⁻
R22.03 The Salt Bridge
- U-tube containing inert electrolyte (KNO₃, KCl).
- Completes internal circuit.
- Maintains electrical neutrality in half-cells.
R22.04 Anode & Cathode
- Anode: Oxidation occurs (Loss of mass).
- Cathode: Reduction occurs (Gain of mass).
- Mnemonic: An Ox and a Red Cat.
22.B — NOTATION & THERMODYNAMICS
ZnZn²⁺||Cu²⁺Cu
R22.05 Cell Notation
- Shorthand for cell structure.
- Anode (Oxidation) always on the Left.
- Cathode (Reduction) always on the Right.
- Double line (||) represents salt bridge.
E°=E°(red)-E°(ox)
R22.06 Standard Cell Potential
- $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$.
- Measured under standard conditions (1M, 1 atm, 298K).
- Positive E° means spontaneous reaction.
R22.07 The Daniell Cell
- Classic example of a Galvanic cell.
- Zinc anode in ZnSO₄, Copper cathode in CuSO₄.
- Produces standard potential of 1.10 Volts.
e⁻ →
← I
R22.08 Flow Dynamics
- Electrons flow Anode → Cathode.
- Conventional Current (I) flows Cathode → Anode.
- Ions flow through salt bridge to balance charge.
22.C — KINETICS & COMMERCIAL CELLS
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R22.09 Reversible Cells
- Can be driven backwards by applying $V_{ext} > E_{cell}$.
- Acts as Galvanic when discharging.
- Acts as Electrolytic when charging.
R22.10 Overpotential
- Voltage required in excess of thermodynamic value.
- Needed to overcome kinetic activation barriers.
- Crucial in industrial electrolysis design.
m∝Q
R22.11 Faraday's Laws
- Mass deposited is proportional to charge passed ($Q = It$).
- 1 Faraday (96,485 C) deposits 1 equivalent weight.
- Dictates efficiency of electroplating.
&
R22.12 Commercial Cells
- Primary: Non-rechargeable (Dry cell / Leclanché).
- Secondary: Rechargeable (Lead-acid, Li-ion).
- Require specialized porous separators and casing.