Displacement reactions

In a nutshell

Displacement reactions involve a more reactive metal displacing a less reactive metal present in a compound. In this lesson you will learn about why displacement reactions occur as well some examples.

Displacement

Displacement reactions involve a more reactive metal and a compound which contains a less reactive metal.

When a reactive metal comes into contact with the compound it displaces (pushes out and takes the place of) the less reactive metal.

The less reactive metal that is displaced is not bound to other elements and therefore exits as a pure element.

Reactivity

Metals have different reactivities: some are reactive, some are are unreactive and some are completely inert.

Examples

Magnesium is a reactive metal. When magnesium is heated it readily reacts with oxygen in the air.

Platinium is inert and will not react with oxygen even at high temperatures, therefore platinium is a good substance to use in fine jewellery and surgical tools.

Reactivity series

The reactivity series shows metals in order of reactivity, with the most reactive at the top and the least reactive at the bottom.

Science; Chemical reactions; KS3 Year 7; Displacement reactions

Reactions

Displacement reactions can be carried out to determine the reactivity of metals. This involves placing a metal into a salt solution and observing what happens.

A change is colour indicates that a displacement reaction has occurred.

Example

Copper sulfate is a blue solution but when zinc is added to it, the solution turns colourless. This is because a displacement reaction occurs and zinc sulfate, a colourless compound, forms.

$zinc(s) \space + \space copper \space sulfate(aq) \rightarrow zinc\space sulfate(aq) \space + \space copper(s)$

$Zn(s) \space + CuSO_4(aq) \rightarrow ZnSO_4(aq) + \space Cu(s)$

Example

When copper is added to a solution of magnesium chloride, no reaction occurs and no change is observed. This is because copper is less reactive than magnesium and cannot displace it from its salt.