Electrolytic Cells
Definition and meaning of Electrolytic Cells in chemistry.
Electrolytic cells use electricity from an outside power source to force a chemical reaction that would not happen on its own. They turn electrical energy into chemical energy, which is the opposite of what a battery does.
In more detail
A power source pushes electrons through the circuit. This forces oxidation to happen at the anode and reduction to happen at the cathode, running the reaction backward from how it would go naturally. Because the reaction does not want to happen, the applied voltage has to be strong enough to overcome the cell's natural resistance to it.
Electrolytic cells power electrolysis, electroplating, and metal refining. They also drive major industrial processes. These include the chlor-alkali process, which makes chlorine and sodium hydroxide, and the Hall-Heroult process, which produces aluminum metal from its ore.
A common misconception is that electrolysis always produces the same products no matter which electrolyte is used. In reality, the products depend heavily on which ions are present and how easily each one gives up or gains electrons. Electroplating is one of the most familiar everyday uses of electrolytic cells.
A thin layer of metal, such as chromium or gold, is deposited onto an object's surface to improve its appearance or resist corrosion. The object being plated acts as the cathode, so the desired metal ions in solution are reduced and stick to its surface.
For example, electrolyzing water with dissolved salt produces different gases than electrolyzing pure water alone. The salt ions react more easily than water molecules do.
Key facts
| Field | Physical Chemistry |
|---|---|
| Energy Conversion | Electrical energy to chemical energy |
| Anode | Oxidation, connected to the positive terminal |
| Cathode | Reduction, connected to the negative terminal |
| Requires | An external power source |
| Example Processes | Chlor-alkali process, Hall-Heroult aluminum production |
In the electrolysis of molten sodium chloride, an outside voltage source pulls electrons toward the cathode. There, sodium ions (Na+) gain electrons and become liquid sodium metal. At the same time, chloride ions (Cl-) lose electrons at the anode and become chlorine gas.
Frequently asked questions
How does an electrolytic cell differ from a galvanic cell?
A galvanic cell generates electrical energy from a reaction that happens on its own. An electrolytic cell uses outside electrical energy to force a reaction that would not happen by itself.
Which electrode is negative in an electrolytic cell?
The cathode is negative because it is wired to the negative terminal of the outside power supply. This is the opposite of a galvanic cell, where the cathode is positive.
What happens if you don't apply enough voltage?
If the applied voltage is too low, it cannot overcome the reaction's resistance to happening, so the reaction simply will not run. Electrolysis only starts once the voltage passes a minimum threshold.