Electrochemistry Lecture Notes

Electrolytic Cells

• Definition: A non-spontaneous reaction driven by an external power source.
• Characteristics:
  • Increases free energy; not spontaneous.
  • Requires an external potential greater than the cell's negative potential (like using a battery).
  • Requires overpotential to drive the reaction.

Overpotential

• Definition: Extra potential required to drive a non-spontaneous reaction.
• Importance:
  • Acts like activation energy.
  • Can be beneficial when differentiating between reactions with similar potentials but different overpotentials.

Galvanic vs. Electrolytic Cells

• Galvanic Cell: Spontaneous discharges occur.
• Electrolytic Cell: Non-spontaneous recharges occur by reversing the cell.
• Key Changes When Reversing:
  • All arrows switch direction (electrons, ions, plating/eroding).
  • Anode and cathode switch places.
  • Source and sink of electrons move to the power supply.

Electrolysis of Water

• Objective: Split water into hydrogen and oxygen gases.
• Setup: Uses a power supply to drive a non-spontaneous reaction.
• Observations:
  • Twice as much hydrogen gas is produced as oxygen.
  • pH changes indicated by universal indicators around electrodes.
  • Demo conducted in a single container.

Electroplating Example

• Objective: Plate copper onto a brass key.
• Process:
  • Copper ions reduce to metal on the key (cathode).
  • Copper strip oxidizes to ions (anode).
  • Calculations for theoretical plating based on current and time.

Metal Ores and Corrosion

• Metal Ores: Metals often found as cations in nature due to oxidation.
• Smelting: The process of reducing cations to elemental metal form.
• Corrosion: Natural oxidation of metals back to cations.

Cathodic Protection

• Method: Attach a more easily oxidized metal (sacrificial anode) to protect another metal (cathode).
• Applications: Protecting structures like pipes and ships.

Coatings and Alloys

• Coatings: Prevent oxidation by acting as barriers (e.g., galvanization).
• Self-forming Coatings: Form naturally on metals like aluminum, preventing further oxidation.
• Alloys: Mixtures with altered properties, including different reduction potentials.

Example: Stainless Steel

• Composition: Iron, carbon, chromium, nickel.
• Properties: Enhanced hardness, corrosion resistance.

Summary

• Electrolytic and galvanic cells serve different purposes based on spontaneity.
• Overpotential and applied potentials drive electrolytic processes.
• Metallurgy involves reducing ores and preventing corrosion through various methods.

Next, we will explore coordinate covalent complexes.