Note: The displacement reactions, in which highly reactive metals such as sodium, calcium, aluminium etc. are used as reducing agents because they can displace metals of lower reactivity from their compounds.
For example, when manganese dioxide is heated with aluminium powder, the reaction that takes place is:
3MnO2(s) + 4Al(s) → 3Mn(l) + 2Al2O3(s) + heat
These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state.
•The reaction of iron (III) oxide (Fe2O3)with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as thermit reaction.
Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + heat