What is a thermite reaction? Explain with the help of an equation. State one use of this reaction.

The reduction of a metal oxide to form metal by using aluminium powder as a reducing agent is called thermite reaction.

 Aluminium reduces iron oxide to produce iron metal with the evolution of a lot of heat (magnesium ribbon is used as a catalyst).

$Fe_2O_3(s) + 2Al(s) → 2Fe(l) + Al_2O_3(s) + Heat$

Due to this heat, iron metal is produced in the molten state. This molten iron is then poured between the broken iron pieces to weld them.

This property of reduction by aluminium is used in thermite welding for joining the broken pieces of heavy iron objects like girders etc.