In electrolysis, the chemical reactions that occur at each electrode can be described by half equations. These equations represent the oxidation or reduction processes happening at the anode and cathode, respectively. Each half equation shows the movement of electrons and the conversion of ions into their elemental forms.

Half Equations at the Electrodes

1. At the Cathode (Reduction Reaction):

• Aluminium ions $\ce(Al^3+)$are attracted to the cathode, where they gain electrons to form aluminium metal.

• The half equation for this reduction is: $\ce{Al3+ +3e^−→Al(l)}$

• Here, the aluminium ion gains three electrons (3e−) to become neutral aluminium $(Al)$.

2. At the Anode (Oxidation Reaction):

• Oxide ions $(O2−)$ are attracted to the anode, where they lose electrons to form oxygen gas.
• The half equation for this oxidation is: $\ce2O^2−→O2(g)+4e^−$
• In this reaction, two oxide ions each lose two electrons, combining to form one molecule of oxygen gas $(O2)$ and releasing four electrons (4e−).

To ensure a half equation is correctly written, it's important to verify that the charges are balanced on both sides of the equation. In the examples above:

Half equations are essential for understanding the detailed process of electrolysis. They allow us to see exactly what is happening at each electrode: