Activity Series : Displacement reactions


A displacement reaction is a reaction: in which an element reacts with a compound,displacing an element from it. Since these reactions involve an element and one of its compoud,these must  be oxidaion-reduction reaction.For example:

Cu (s) +  2AgNO3 (aq) -------------> Cu(NO3)2 (aq)  + 2Ag (s)

From this molecular equation is appears that copper displaces silver in silver nitrate,to produce silver metal and a greenish-blue solution of copper (II) nitrate.However, the net ionic equation shows that the reaction involves the transfer of electrons from copper metal to silver ion:

    Cu (s) + 2Ag + (aq) -----------> Cu^2+ (aq)  + 2Ag (s)

So, the whole point is whether a reaction occurs between a given element and a monoatomic ion depends on the relative ease with which the two species gain or lose electrons.

The table given here shows the activity series  of the elements:


The activity series of the elements is the listing of the elements in decreasing  order of their ease of losing electrons during reaction in aqueous solution.The metals listed at the top are the strongest reducing agents ( they lose electrons easily) and those at the bottom are the weakest.A free elements reacts with the monoatomic  ion of another element if free element ia above the other element     
in the activity series.
Zn(s) + 2 H+(aq) rightarrow H2(g) + Zn2+(aq)
You would expect this reaction to proceed as written because Zince metal Zn is well above hydrogen  in the activity series.

  But magnesium metal can remove zinc ions from solution:

Mg(s) + Zn2+(aq) rightarrow Zn(s) + Mg2+(aq)

The reaction goes nearly to completion.


"The activity series is a useful guide for predicting the products of metal displacement reactions. For example, placing a strip of zinc metal in a copper(II) sulfate solution will produce metallic copper and zinc sulfate, since zinc is above copper on the series. A strip of copper placed into a zinc sulfate solution will not produce an appreciable reaction, because copper is below zinc on the series and can't displace zinc ions from solution".