Chapter 6: Electrochemistry

Chapter 6: Electrochemistry

Redox Reactions

- Oxidation: Loss of electrons/increase in oxidation number.

- Reduction: Gain of electrons/decrease in oxidation number.

- Redox reaction: Both processes occur simultaneously.

- Oxidation numbers help track electron transfer.

Electrolysis

- Definition: Decomposition of a compound using electricity.

- Requires an electrolyte (molten or aqueous ionic compound).

- Electrodes: Conduct electricity; can be inert (graphite, platinum) or reactive.

- At the cathode (negative electrode): reduction occurs.

- At the anode (positive electrode): oxidation occurs.

Electrolysis of Common Compounds

- Molten NaCl → Na metal at cathode, Cl₂ gas at anode.

- Aqueous CuSO₄ → Cu deposited at cathode, O₂ released at anode.

Applications of Electrolysis

- Electroplating: coating objects with a thin layer of metal.

- Purification of metals (e.g., copper).

- Extraction of reactive metals (e.g., aluminium from bauxite).

Electrochemical Cells

- Convert chemical energy into electrical energy.

- Made of two half-cells connected by a salt bridge.

- Electrons flow from the more reactive metal (anode) to the less reactive (cathode).

- Voltage depends on difference in reactivity.

Standard Electrode Potentials (E°)

- Measured relative to the standard hydrogen electrode (SHE).

- Conditions: 298 K, 1 atm, 1 mol/dm³ solutions.

- Positive E° → tendency to be reduced.

- Negative E° → tendency to be oxidized.

Predicting Feasibility of Reactions

- Combine half-cell potentials to calculate overall cell potential.

- If E°cell is positive → reaction is feasible.

- If E°cell is negative → reaction is not feasible.

Fuel Cells

- Generate electricity from chemical reactions, often involving hydrogen.

- Hydrogen-oxygen fuel cell: produces water as only product.

- Advantages: efficient, clean.

- Limitations: storage of hydrogen, cost.