Displacement Reaction or Displacement Reaction: 

A more reactive element (metal) displaces less reactive element (metal) from its aqueous salt soln. 

 For example:

ü  Zn (s)  +   FeSO4 (aq)    →    ZnSO4 (aq) + Fe (s)
                              (green)            (Colourless) 

ü  Fe (s)  +  CuSO4 (aq)    →   FeSO4 (aq)  + Cu (s) ↓
Iron          Blue                     Green            Reddish Brown

ü  Mg (s) +  H2SO4 (aq)    →   MgSO4 (aq) +  H2O (g)
Magnesium    Sulphuric             Magnesium     Water
                                            Acid                    Sulphate

ü  Cu (s)  +  2AgNO3 (aq) →  Cu (NO3)2 (aq) + 2Ag (s).
                         Copper     Silver Nitrate       Copper Nitrate      Silver

ü  KI (aq) +  Cl2 (g)           →  KCl (aq)    +    I2 (g)
 Potassium     Chlorine               Potassium    Iodine
 Iodide                                        Chloride


Double Displacement Reaction 

The chemical reactions in which compounds react to form two different compounds by mutual exchange of ions are called double displacement reactions.

Reactions occurs by two different ways

    ⤭ Precipitation: In such reactions due to exchange of ions some insoluble material is formed. This insoluble material is called precipitate and the reaction is called precipitation reaction. For example:

ü  ZnSO4 (aq)    +   BaCl2 (aq)     →   ZnCl2 (aq)   +  BaSO4 (s)
 Zinc                 Barium                         Zinc                  Barium     
Sulphate          Chloride                        Chloride           Sulphate (White)

ü  2 HCl (aq)      +   Pb(NO3)2(aq) →  2 HNO3 (aq)  +  PbCl2 (s) ↓
             Hydrochloric     Lead                        Nitric              Lead  (White)
       Acid                  Nitrate                      acid                Chloride

ü  Pb(NO3)2(aq)  +   2 KI (aq)        →    PbI2 (aq)  ↓ +   KNO3 (s)
      Lead                      Potassium             lead                  Potassium
      Nitrate                   Iodide                   Iodide               Nitrate

 
v Neutralization Reaction: In this type of reaction an acid reacts with a base to form salt and water by exchange of ions.

ü  NaOH (aq)  + HCl (aq)      →    NaCl (aq)     +    H2O.
Sodium          Hydrochloric        Sodium              Water
Hydroxide      Acid                     Chloride
(Base)             (Acid)                   (Salt)                (Water)

ü  ZnO   +     HNO3    →   Zn(NO3)2   +   H2O
Zinc           Nitric           Zinc                 Water
Oxide        Acid             Nitrate
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