Displacement reactions involve a metal and a compound of a different metal. In a displacement reaction:
Displacement reactions are easily seen when a salt of the less reactive metal is in the solution. During the reaction:
For example, magnesium is more reactive than copper. When a piece of magnesium is dipped into blue copper sulfate solution:
Here are the equations for the reaction:
magnesium + copper sulfate → magnesium sulfate + copper
Mg + CuSO4 → MgSO4 + Cu
No reaction is seen if you do things the other way round – in other words, if you put copper powder into magnesium sulfate solution. This is because copper is not reactive enough to displace magnesium from magnesium sulfate.
You can investigate the reactivity of metals using displacement reactions. The table shows the results from a series of experiments involving four metals and solutions of their salts. A tick shows where there is a visible reaction and a cross shows where there is no visible reaction.
Magnesium displaces three metals, zinc displaces two metals, iron displaces one metal and copper does not displace any of the other three metals. So, the order of reactivity, starting with the most reactive first, is:
Displacement reactions can also involve metal oxides.