17.7 Electrolysis

Electrolysis is a fascinating process that uses electricity to drive chemical reactions. It's all about splitting compounds into their elements or depositing metals onto surfaces. This technique is crucial in many industries, from metal refining to producing important chemicals.

Understanding electrolysis helps us grasp how we can harness electrical energy to make or break chemical bonds. It's a key part of electrochemistry, showing how we can control and manipulate chemical reactions using electricity. Pretty cool stuff!

Electrolysis

Steps and components of electrolysis

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• Electrolysis uses electrical energy from an external power source (battery or electrical outlet) to drive a non-spontaneous redox reaction
• Electrolytic cell components include an electrolyte (ionic compound dissolved in water or molten state) and two electrodes (cathode and anode) submerged in the electrolyte
  • Cathode is the negative electrode where reduction occurs and cations gain electrons
  • Anode is the positive electrode where oxidation occurs and anions lose electrons
• Dissociation of the electrolyte into cations and anions when dissolved or molten
• Migration of ions with cations moving towards the cathode and anions moving towards the anode
• Examples of electrolysis include electroplating (depositing a thin metal layer onto an object), electrolytic refining (purifying metals by separating them from impurities), and production of elements (extracting reactive metals like sodium from their compounds)

Electrolytic vs galvanic cells

• Electrolytic cells require an external power source to drive a non-spontaneous redox reaction, converting electrical energy into chemical energy
  • Reduction occurs at the cathode and oxidation occurs at the anode
  • Applications include electroplating, electrolytic refining, and production of elements
• Galvanic cells (voltaic cells) generate electrical energy from a spontaneous redox reaction, converting chemical energy into electrical energy
  • Reduction occurs at the cathode (positive electrode) and oxidation occurs at the anode (negative electrode)
  • Applications include batteries, fuel cells, and electrochemical sensors
• Key differences between electrolytic and galvanic cells:
  • Energy source (external power vs self-generated)
  • Reaction spontaneity (non-spontaneous vs spontaneous)
  • Energy conversion (electrical to chemical vs chemical to electrical)

Faraday's laws in electrolysis calculations

• Faraday's laws relate the amount of substance produced or consumed during electrolysis to the quantity of electrical charge passed through the cell
• First law states that the mass of a substance altered at an electrode is directly proportional to the quantity of electricity transferred at that electrode
  • Mathematically expressed as $m = kQ$, where $m$ is mass, $k$ is a constant, and $Q$ is charge transferred
• Second law states that the masses of different substances altered by the same quantity of electricity are proportional to their equivalent weights (molar mass divided by the number of electrons transferred per formula unit)
• Calculate the mass of a substance produced during electrolysis using $m = \frac{QM}{nF}$
  • $m$ is mass, $Q$ is charge passed (coulombs), $M$ is molar mass, $n$ is number of electrons transferred per formula unit, and $F$ is Faraday's constant (96,485 C/mol)
• Calculate the volume of a gas produced during electrolysis using the ideal gas law $PV = nRT$
  • $P$ is pressure, $V$ is volume, $n$ is number of moles (calculated using Faraday's laws), $R$ is gas constant, and $T$ is temperature

Electrochemistry fundamentals

• Electrochemistry is the study of chemical processes that cause electrons to move, including electrolysis and galvanic cells
• Oxidation-reduction reactions (redox reactions) involve the transfer of electrons between species
• Half-reactions describe the separate oxidation and reduction processes occurring at each electrode
• Electrolytes are substances that conduct electricity when dissolved in water or molten, due to the presence of ions
• Electrical conductivity of an electrolyte solution depends on the concentration and mobility of ions present