Displacement Reaction : Single and Double Displacement Reactions

Displacement reactions are very important chemical reactions of chemistry. They are used in many ways in various fields. For example, we use electroplating to prevent iron objects from rusting which is based on displacement reaction.


What is Displacement Reaction? 

The type of reaction in which part of one reactant is displaced by another reactant is called displacement reaction. It is also called a  replacement reaction. As replacement of one ion of reactant takes place by another ion of reactant. 

Example – Fe + CuSO4 🡪 FeSO4 + Cu

There are two types of displacement reactions –

  • Single displacement reaction 

  • Double displacement reaction 


What is Single Displacement Reaction?

Those reactions in which one element replaces another element from its salt or compound are called single displacement reactions. These are also called single replacement reactions. General representation can be written as well –

A + B-C 🡪 A-C + B

It will occur if A is more reactive than B. Generally, metals and its salts give single displacement reactions. In these reactions more reactive metal displaces less reactive metal from its salt. For example, potassium is more reactive than magnesium, so potassium replaces magnesium from magnesium chloride. The reaction between potassium and magnesium chloride occurs as follows –

2K + MgCl2 🡪 2KCl + Mg


What is Reactivity Series? 

Reactivity series is the series of metals based on their reactivity from highest to lowest. So, reactivity series of metals can be defined as a series of metals, in order of reactivity from highest to lowest. It is also known as activity series. The reactivity of metals is because of their incomplete outer orbitals or due to their electronic configuration. Metals form positively charged ions as they tend to lose electrons. Metals with high atomic numbers tend to be more reactive as their electrons are far from the positively charged nucleus. So, they can be removed easily.


Reactivity Series of Metals is Given Below - 

Symbol of element 

Name of element 


Potassium 


Most Reactive 

Na 

Sodium 






↓Reactivity decreases


Ca

Calcium 

Mg 

Magnesium 

Al 

Aluminium 

Zn 

Zinc 

Fe 

Iron 

Pb 

Lead 

Hydrogen 

Cu

Copper 

Hg

Mercury 

Ag 

Silver 

Au 

Gold 

Pt 

Platinum 

Least reactive 


Hydrogen is a non-metal but still it has been included in the reactivity series as it helps in the comparison of reactivity of metals. 

What is Double Displacement Reaction? 

Double displacement reactions are those reactions where the cations and anions of reactants switch places with each other or replaces each other. Generally, it can be represented as follows –

AB + CD 🡪 CB + AD

Example of double displacement reaction – Reaction between silver nitrate and sodium chloride is an example of double displacement reaction. The reaction given below –

AgNO3 + NaCl 🡪 AgCl + NaNO3

Examples of Displacement Reactions 

  • Examples of single displacement reaction –

  • Reaction between zinc and copper sulphate –

                         Zn + CuSO4 🡪 ZnSO4 + Cu

  • Reaction between copper and silver nitrate –

                         Cu + 2AgNO3 🡪 CuNO3 + 2Ag

  • Reaction between iron and copper sulphate –

                         Fe + CuSO4 🡪 FeSO4 + Cu

  • Reaction between lead and copper chloride –

                        Pb + CuCl2 🡪 PbCl2 + Cu

  • Reaction between chlorine and sodium bromide –

                        Cl2 + 2NaBr 🡪 2NaCl + Br2

  • Examples of double displacement reaction -

  • Reaction between potassium nitrate and aluminum chloride –

                         KNO3 + AlCl3 🡪 Al(NO3)3 + KCl

  • Reaction between lead nitrate and potassium iodide –

                        Pb(NO3)2 + 2KI 🡪 2KNO3 + PbI2

  • Reaction between iron chloride and barium hydroxide –

                        FeCl3 + Ba(OH)2 🡪 Fe(OH)3 + BaCl2 

  • Reaction between lead nitrate and sodium sulphate –

                          Pb(NO3)2 + Na2SO4 🡪 PbSO4 + 2NaNO3 

  • Reaction between barium chloride and copper sulphate –

                         BaCl2 + CuSO4 🡪 BaSO4 + CUCl2


Applications of displacement reactions 

Displacement reactions have many applications in various fields. Some of them are given below –

  • It is used in thermite welding. In which aluminum displaces iron from its oxide.

  • It is sued in steel making. In which carbon displaces iron from its oxide.

  • It is largely used in extraction of metals. 

  • It is used in acid indigestion. 

  • It is used in flame photometry. 

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