Electrolysis
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Topic Summary & Highlights
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Core Concept
Electrolysis is a process that uses an electric current to induce a chemical reaction that would not occur spontaneously.
Key Purpose: Convert electrical energy into chemical energy.
Practice Tips
Electrolysis uses electrical energy to drive non-spontaneous reactions.
Reduction occurs at the cathode; oxidation occurs at the anode.
Faraday’s laws relate the amount of substance produced to the current and time.
Applications include metal extraction, electroplating, water splitting, and refining.
Components of an Electrolytic Cell
Power Source:
Provides the electric current necessary to drive the reaction.
Electrodes:
Cathode:
Site of reduction (gain of electrons\text{gain of electrons}gain of electrons).
Connected to the negative terminal of the power supply.
Anode:
Site of oxidation (loss of electrons\text{loss of electrons}loss of electrons).
Connected to the positive terminal of the power supply.
Electrolyte:
Ionic solution or molten compound that conducts electricity by allowing ions to move.
Key Concepts
Reduction at the Cathode:
Positive ions (cations\text{cations}cations) gain electrons to form neutral atoms.
Example: Na++e−→Na\text{Na}^+ + e^- \rightarrow \text{Na}Na++e−→Na.
Oxidation at the Anode:
Negative ions (anions\text{anions}anions) lose electrons to form neutral atoms or molecules.
Example: 2Cl−→Cl2+2e−2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^-2Cl−→Cl2+2e−.
Energy Requirement:
Electrolysis requires energy input because the reactions are non-spontaneous.
Faraday’s Laws of Electrolysis
First Law:
The mass (mmm) of a substance produced at an electrode is proportional to the amount of charge (QQQ) passed through the electrolyte.
m=Z⋅Q
Where:
Z: Electrochemical equivalent (g/C\text{g/C}g/C).
Q: Charge (C\text{C}C).
Q=I⋅t, where I is current (A) and t is time (s).
Second Law:
For the same amount of charge, the mass of different substances produced is proportional to their molar masses divided by the number of electrons transferred per ion (n):
$m \propto \frac{M}{n}$