Question

Define displacement reaction. Give two examples of it. How it is different from a double displacement reaction.

Answer 1

Hint : In displacement reaction, displacement of less reactive element takes place the more reactive element. But in a double displacement reaction, the ions of reactants exchange their places to form a new product. Double displacement reaction is also called salt metathesis.

Complete Step By Step Answer:
In displacement reaction, both metal and non-metal take part and the less reactive element gets replaced by the more reactive element. So it is also called a replacement reaction or a metathesis reaction. Displacement reactions are of two types:
Single displacement reaction
Double displacement reaction

If we assume the given reaction we can simply understand the single displacement reaction:
  $AB+C\to AC+B$
Here, we can see that $C$ replaces the $B$ metal and forms a new product. This reaction is called a single displacement reaction.
Reactivity of elements is given by reactivity series of metal (a recorded data) given as:
 $K>Na>Ca>Mg>Al>Zn>Fe>Pb>Sb>Cu>Hg>Ag>Au$
Going from the right to the left of the table the metals:
increase in reactivity;
lose electrons (oxidize) more readily to form positive ions;
corrode or tarnish more readily;
require more energy (and different methods) to be isolated from their compounds;
become stronger reducing agents (electron donors).
Two examples of displacement reactions are:
The reaction between iron and copper sulphate to give iron sulphate as product.
 $Fe+CuS{O}_4\to FeS{O}_4+Cu$
Here, iron displaces copper because iron is more reactive than copper.
The reaction between zinc and iron sulphate to give zinc sulphate as a product.
 $Zn+FeS{O}_4\to ZnS{O}_4+Fe$
Here, zinc displaces iron because zinc is more reactive than iron.
In a double displacement reaction, the exchange of two ionic species takes place between two different molecules. For example, the reaction of copper chloride with silver nitrate to form copper nitrate and silver chloride as products.
 $CuC{l}_{2(aq)}+2AgN{O}_3\to Cu(N{O}_3{)}_2+2AgCl$
It is different from a single displacement reaction because it occurs when there are exchangeable ions present in the compound. In double displacement reaction mostly precipitate forms.

Note :
In single displacement reaction only one chemical species gets displaced and only one chemical species gets replaced while in double displacement reaction two ions get displaced and two ions get replaced. It is the most common point of differentiation between both types.