The Thermite Reaction

The Thermite Reaction is a popular demonstration in school science lessons. This is for two main reasons:

1. It gives a spectacular firework-like explosion.

2. It demonstrates an important concept in chemistry: the competition between metals of different reactivity.

It is done by carefully mixing a measured amount of dry iron(III) oxide powder with another measured amount of aluminium powder. This mixture is ignited, usually by a piece of magnesium ribbon and some magnesium powder.

The magnesium burns with enough heat to initiate the reaction. The reaction proceeds with lots of sparks and flames and leaves behind a lump of molten iron metal.

This reaction is a classic example of an exothermic redox reaction!

This means that the reaction produces energy by rearranging chemical compounds to form different ones. The reaction starts with an element (aluminium) and a compound (iron oxide). It is ignited by a reaction that produces a lot of heat. Then the atoms rearrange themselves into a different element (iron) and a different compound (aluminium oxide). A lot of energy is produced in the form of light and heat.

The chemical equation is:

Fe₂O₃ + 2Al --> Al₂O₃ + 2Fe

This simply means that one molecule of iron(III) oxide reacts with two atoms of aluminium to form one molecule of aluminium oxide and two atoms of iron metal.

The reaction is called a "redox" reaction because the iron is "reduced" from being bound to oxygen to being a free atom. The aluminium, on the other hand, has been "oxidised" - it has gone from being a free atom to being bound to oxygen.

Heat is produced in the reaction, it is "exothermic". This is because aluminium is a more reactive metal than iron, it prefers to be bound to other elements so energy is released when it reacts with iron oxide.

The Thermit Reaction has been used in various important applications.

It is used to weld sections of steel together in-place. For example, the mixture can be placed between sections of railway track and ignited, welding the tracks toegther.

It is also used in times of war. During the Second World War, for example, after D-day when the Allied troops were seeking to disable German artillary, instead of wasting explosives they used the Thermite mixture to weld the parts of the guns together.