Oxidation half-reaction and reduction half reaction
In a chemical reaction, when an atom or molecule loses one or more electrons, it undergoes oxidation, while when an atom or molecule gains one or more electrons, it undergoes reduction. These two processes occur simultaneously in what is known as a redox (reduction-oxidation) reaction.
To represent a redox reaction, it is often written as two half-reactions, one for oxidation and one for reduction. These half-reactions show how electrons are transferred between reactants and products.
For example, the reaction between magnesium (Mg) and oxygen (O2) to form magnesium oxide (MgO) is a redox reaction, which can be written as:
2Mg + O2 → 2MgO
The oxidation half-reaction is:
Mg → Mg2+ + 2e-
This shows that magnesium atoms lose two electrons to become positively charged magnesium ions.
The reduction half-reaction is:
O2 + 4e- → 2O2-
This shows that oxygen molecules gain four electrons to become negatively charged oxide ions.
By combining these two half-reactions, we can see that the magnesium atoms lose electrons, while the oxygen molecules gain electrons, as they react to form magnesium oxide.