In a displacement reaction, an element that is more reactive pushes out (displaces) an element that is less reactive. Below is an example of a displacement reaction between iron and copper sulphate:
In this scenario, we can say that the iron (Fe) displaced copper (Cu), as it has swapped positions with copper. Iron is now bonded to the sulphate (SO4) to form iron sulphate (FeSO4), while the metal in the solution has become copper, which is now on its own.
The word equation for this reaction is:
Iron + Copper sulphate → Iron sulphate + Copper
These reactions take place due to differences in reactivity. Let’s take a look at the reactivity series:
For a displacement reaction to take place, the element on its own must be more reactive than the element that is in the compound.
In our earlier example, iron, which is on its own, is more reactive than copper, which is part of the copper sulphate solution. This is why the iron replaces the copper and we end up with iron sulphate (FeSO4).
Let’s look at an example that wouldn’t work:
Iron + Magnesium sulphate →
Fe + MgSO4 →
As iron is more reactive than magnesium, it won’t displace magnesium, and therefore the reaction won’t occur.