2.31    deduce the position of a metal within the reactivity series using displacement reactions between metals and their oxides, and between metals and their salts in aqueous solutions

A reactive metal will displace a less reactive metal from its oxide.  These reactions are often known as thermit reactions.  A good example is the reaction between aluminium and iron (III) oxide:

2Al(s)  +  Fe2O3(s)  ®   Al2O3(s)    +   2Fe(s)

These reactions are very vigorous and exothermic once they get started (a special fuse is needed to start them).  In the example above, the temperature rises above 2000^OC and the iron and aluminium oxide are formed in the molten liquid state!  The further apart in reactivity the metals are, the more violent the reactions become, so Mg and CuO would be very dangerous!

Similarly, a more reactive metal will displace a less reactive metal from one of its salts.

e.g. 1    zinc will displace copper from a solution of copper (II) sulfate

            Zn(s) + CuSO4(aq)   →   ZnSO4(aq) + Cu(s)

In the above reaction we see the solution go from blue to colourless and the grey zinc gets covered in brown copper. These displacement reactions are exothermic.

e.g. 2    iron cannot displace magnesium from a solution of magnesium sulfate, since Fe is less reactive than Mg.