Question

What is displacement reaction?

Answer 1

• Reaction in which a more reactive element displaces a less reactive element for its compound is called displacement reaction.

Answer 2

Displacement reactions occur when a metal from the electrochemical series is mixed with the ions of a metal lower down in the electrochemical series. The atoms of the more reactive metal push their electrons on to ions of the less reactive metal.

Displacement reactions

Displacement reactions occur when a metal from the electrochemical series is mixed with the ions of a metal lower down in the electrochemical series. The atoms of the more reactive metal push their electrons on to ions of the less reactive metal.

The atoms of the reactive magnesium give away electrons.


M
g
(
s
)
→
M
g
2
+
(
a
q
)
+
2
e
−

(
M
g
(
s
)
= silvery metal atoms)

(
M
g
2
+
(
a
q
)
= colourless soluble metal ions)

The ions of the less reactive copper are forced to accept these electrons.


C
u
2
+
(
a
q
)
+
2
e
−
→
C
u
(
s
)

(
C
u
2
+
(
a
q
)
= blue ions)

(
C
u
(
s
)
= brown metal powder)

The overall equation for the displacement of copper by magnesium is:


M
g
(
s
)
+
C
u
2
+
(
a
q
)
→
M
g
2
+
(
a
q
)
+
C
u
(
s
)

Hint: Notice that there are sometimes colour changes during displacement reactions, depending on the reactants and the products involved. Ion-electron equations for half reactions like these are given in the data booklet.

Some other examples of displacement reactions which can occur are:

zinc displacing iron ions from iron(II) sulfate solution
nickel displacing copper from copper(II) nitrate solution
copper displacing silver from silver(I) nitrate solution
The higher up metal in the electrochemical series always displaces the ions of the lower down metal. Low down metals in the series cannot displace more reactive metals from their solutions. You can use this idea to predict whether a displacement reaction will occur.