In an oxidation reaction, a substance gains oxygen. Oxidation reactions typically occur when a substance reacts with oxygen, which produces an oxide. An example of an oxidation reaction is combustion, in which a fuel reacts with oxygen to produce energy.
When a metal or a non-metal reacts with oxygen, this is also an oxidation reaction.
When a metal reacts with oxygen, it produces a metal oxide, and the general equation for this is:
Metal + Oxygen → Metal oxide
Metal oxides are formed when metals react with oxygen. They are bases which react with acids and neutralise them. Some metal oxides dissolve in water to form alkaline solutions.
An example of a metal reacting with oxygen is when magnesium reacts with oxygen to form magnesium oxide. The word equation for this reaction is:
Magnesium + Oxygen → Magnesium oxide
The symbol equation for this reaction is:
2Mg + O2 → 2MgO
For reactive metals, heat isn’t required for them to react with oxygen. When they are exposed to the air, they will react with oxygen in the air, which will develop an outer oxide later around the metal.
You will be able to see that the oxide layer has developed as it is often a different colour. The oxide layer acts as a protective layer, preventing the metal underneath from undergoing further oxidation.
Different metals have varying levels of reactivity with oxygen. Some metals, such as copper, are less reactive and require heat to initiate an oxidation reaction. For example, heating copper over a Bunsen burner flame will form a copper oxide layer on its surface.
On the other hand, more reactive metals like magnesium will produce a more vigorous reaction when heated. When magnesium is burned in the air, it reacts with oxygen to form magnesium oxide, releasing intense heat and light.
Non-metals react with oxygen to form non-metal oxides. For example, carbon reacts with oxygen to form carbon dioxide.
Another example is sulphur, which reacts with oxygen to form sulphur oxide. The word equation for this is:
Sulphur + Oxygen → Sulphur oxide
The symbol equation for this is:
2S + O2 ⮕ 2SO