5.2 Displacement Reactions

5.2 Displacement Reactions

The reactivity series helps to show which metals are more reactive than others. To remember the reactivity series, remember this sentence: "please stop calling me a zebra in the little classroom" The main idea for displacement reactions is: a more reactive metal will displace a less reactive metal from an aqueous solution of one of its salts.

What is a displacement reaction? A displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from it's compound. Both metals and nonmetals take part in displacement reactions.

For example: Magnesium is more reactive than copper, so when the two react: copper sulphate + magnesium → magnesium sulphate + copper 

In the previous reaction, magnesium displaced copper. Originally, copper was in an aqueous solution of one of its salts, but because magnesium was more reactive, it "took copper's place" in the reaction.  However, if a more reactive metal is in a solution of one of its salts and is reacting with a less reactive metal, there is no reaction. 

For example: magnesium sulphate + copper → no reaction  This is because magnesium is more reactive than copper and so copper can not displace it.

Sometimes, displacement reactions are written in the form of ionic equations. An ionic equation shows only the atoms and ions that change during a reaction.  for example, in this reaction: Mg + CuSO4 → MgSO4 + Cu

The SO4 ions remain the same,  do not appear in the ionic equation. The ionic equation would be: Mg (s) + Cu 2+ (aq)  → Mg 2+ (aq) + Cu (s)  Note: the numbers are supposed to be small.

Another example: zinc + lead nitrate → zinc nitrate + lead  Zinc is more reactive than lead so it displaces lead from a solution of its salt. You will see the lead metals forming as crystals on the zinc.

hydrogen and carbon in the reactivity series

You can include nonmetals hydrogen and carbon in the reactivity series using displacement reactions. You can think of the: Metal + acid → salt + hydrogen reactions as displacement of hydrogen ions, H+, from solution. Other non metals can be put in the reactivity series, just as metals can, for example, carbon.