CBSE Class 10 Answered

The reduction of a metal oxide to form metal by using aluminium powder as a reducing agent is called a thermite reaction. It is an exothermic reaction in which a large amount of heat is evolved. This reduction property of  aluminium is used in thermite welding for joining the broken pieces of heavy iron objects like girders, railway tracks or cracked machine parts.

Example: A mixture of iron (III) oxide and aluminium powder is ignited with a burning magnesium ribbon. Aluminium reduces iron oxide to produce molten iron metal with the evolution of  heat.

Fe₂O_3(s) + 2Al_(s) → 2Fe_(l) + Al₂O_3(s) + Heat

The molten iron produced is then poured between the broken iron pieces to weld them.