Final answer:
Molten electrolysis is rarely used due to high energy demands and complex requirements like high temperatures, as well as differences in electrode potentials compared to standard conditions. The Down's cell electrolysis of molten sodium chloride is an example of its complexity, where hydrogen gas production is avoided to isolate sodium metal.
Step-by-step explanation:
Molten electrolysis is rarely seen or used due to the high energy requirements and significant differences in electrode potentials for molten salts as opposed to their aqueous solutions. Specifically, the energy required to remove electrons from a filled core is prohibitively large under normal reaction conditions, making it energetically less favorable.
Additionally, oxide ions tend to react with oxidized carbon at the anode during the process, resulting in the production of CO₂ gas. This is different from the standard cell potentials listed for the reduction of hydrated ions under standard conditions in aqueous solutions. The electrolysis of molten salts requires conditions very different from standard ones, such as high temperature, which is necessary to melt the salts like NaCl. This makes the setup more complex and expensive compared to electrolysis in aqueous solutions. For instance, when isolating sodium metal through the electrolysis of molten sodium chloride using a Downs cell, it is not feasible to use aqueous solutions of sodium salts due to the easier reduction of hydrogen ions in such solutions, which would produce hydrogen gas at the cathode instead of the desired sodium metal.
The applications of electrolysis are more familiar in contexts such as battery recharging, refinement of metallic ores, manufacture of commodity chemicals, and electroplating. However, despite its commercial and industrial applications, the process of electrolysis in molten salts remains rarer due to the complexities and high costs involved.