The use of electric current to stimulate a non-spontaneous reaction. Electrolysis can be used to separate a substance into its original components/elements and it was through this process that a number of elements have been discovered and are still produced in today's industry. In Electrolysis, an electric current it sent through an electrolyte and into solution in order to stimulate the flow of ions necessary to run an otherwise non-spontaneous reaction. Processes involving electrolysis include: electro-refining, electro-synthesis, and the chloro-alkali process.
Electrolytic Cell vs Voltaic Cell
Example: When we electrolyze water by passing an electric current through it, we can separate it into hydrogen and oxygen.
2H2O(l)→2H2(g)+O2(g)
More information : The Electrolysis of Water
An electrolytic cell is essentially the non-spontaneous reaction's voltaic cell, (in fact if we reversed the flow of electricity within a voltaic cell by exceeding a required voltage, we would create an electrolytic cell). Electrolytic cells consist of two electrodes (one that acts as a cathode and one that acts as an anode), and an electrolyte. Unlike a voltaic cell, reactions using electrolytic cells must be electrically induced and it's anode and cathode are reversed (anode on the left, cathode one the right).
Voltaic Electrolytic
Oxidation: X → X+ + e- (Negative Anode) Y → Y+ + e- (Positive Anode)
Reduction: Y+ + e- → Y (Positive Cathode) X+ + e- → X (Negative Cathode)
Overall: X + Y+→ X+ + Y (G<0) X+ + Y → X + Y+ (G>0)
This reaction is spontaneous and will release energy This reaction is non-spontaneous and will absorb energy
Factors Affecting Electrolysis Reactions
Overpotential- The generated voltage is significantly higher than expected. An overpotential may be necessary to overcome interactions taking place on the electrode itself (especially for gasses).
Electrode type- An inert electrode acts as a surface for a reaction to occur on and is not involved in the chemical reaction whereas an active electrode becomes a part of the half reaction.
Simultaneous electrode reactions- If two different pairs of half-reactions take place at once. Some half reactions should be eliminated in order to determine a single pair of half reactions best suited for the electrolysis to occur.
The state of reactants- If reactants are in nonstandard states, the voltage of half cells may differ from that of the standard amount. In this case, the solution for the anode half cell may have a pH that is either higher or lower than the standard pH of 4 which may lead to a nonstandard voltage as well.
Calculations
Faraday's Constant-The amount of electric charge associated with one mole of electrons.
Faraday's Constant: 1 mole e- = 96,485 C (where C measures Coulombs)
To find the amount of moles of electrons that have been involved in an electrolysis reaction use the following equation:
Charge (C)= current (C/s) x time (s) x (1 mole e-/96,485 C)
Application
Several processes of electrolysis are used in today's industry:
Electrorefining
the anode is the impure metal and any impurities are removed during the process of electrolysis when the metal travels from anode to cathode. During the electrorefining of metals, the cathode has a decomposition of pure metals from a solution containing the metal ion. For example copper is purified through electrolysis in order to be used for applications that require high electrical conductivity. During this process, the cathode is a pure piece of copper, while the anode is an impure piece of copper. The Cu2+ from the anode moves through a sulfuric acid-copper(II) sulfate solution into the cathode where it becomes solid copper. While this is occurring, the impurities are left at the bottom of the tank. This leftover residue is called anode mud. The electrolysis is carried out at 0.15 - 0.30V (low voltage) in o
