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    Home » Chemical Reactions And Equations Notes – Combination, Decomposition, Displacement And Double Displacement reactions

    Chemical Reactions And Equations Notes – Combination, Decomposition, Displacement And Double Displacement reactions

    Dr. Vikas JasrotiaBy Dr. Vikas JasrotiaSeptember 19, 2020No Comments
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    Combination, Decomposition, Displacement And Double Displacement reactions

    Types of Chemical Reactions:

    i). Combination Reaction

    ii). Decomposition Reaction

    a). Thermal Decomposition

    b). Electrolytic Decomposition

    iii). Displacement Reaction OR Substitution reaction

    iv). Double Displacement Reaction            

                   a). Precipitation Reaction            

                   b). Neutralisation Reaction         

    v).  Redox Reaction

    vi). Oxidation Reaction

    vii). Reduction Reaction

    viii). Endothermic Reaction

    ix). Exothermic Reaction

    Explanation of the types of Chemical reactions i.e Combination, Decomposition, Displacement And Double Displacement reactions using examples:

    i). Combination Reaction:


    The reactions in which two or more substances combine to form a new substance are called combination reactions. For example:

    a).  2 Mg (s)    +     O2 (g)     →  2 MgO     

    Magnesium      Oxygen         Magnesium oxide (White ash)

                                                            (basic) turns red litmus blue                                                    

    b). In the laboratory, iron sulphide is prepared by mixing iron and sulphur.

        Fe(s)   + S(s)    →   FeS(s)

    c). Burning of carbon monoxide in oxygen to form carbon dioxide.   

           2CO (g)       +   O2(g)  →       2CO2 (g)

    d).  Calcium oxide upon reaction with water produces calcium hydroxide.

    CaO                +            H2O        →    Ca(OH)2      

    Calcium Oxide       Water           Calcium Hydroxide       

    (Quick Lime)                                (Slaked Lime)

     

    ii). Decomposition reactions:

    These are opposite to combination reactions. A single compound decomposes or break down to give two or more simpler substances.
    It is of following types:

    i).Thermal Decomposition:
    When a decomposition reaction is carried out by heating. 
    For Example:

    • Mercuric oxide, when heated, undergoes thermal decomposition, to give mercury and oxygen

     

     

     

     

     

    iii). Displacement Reaction OR Substitution reaction: 

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

    • Zn (s)  +   FeSO4 (aq)    →    ZnSO4 (aq) + Fe (s)                             

                              (green)               (Colourless) 

    • Fe (s)  +  CuSO4 (aq)    →    FeSO4 (aq)  + Cu (s) ↓

               Iron        Blue                   Green            Reddish Brown

    • Mg (s)        +    H2SO4 (aq)     →   MgSO4 (aq) +  H2O (g)

           Magnesium    Sulphuric             Magnesium     Water                                           

                                       Acid                        Sulphate

    • Cu (s)     +     2AgNO3 (aq)      →   Cu (NO3)2 (aq)    +   2Ag (s).                        

           Copper            Silver Nitrate      Copper Nitrate      Silver

    • KI (aq)      +    Cl2 (g)           →  KCl (aq)    +    I2 (g) 

           Potassium     Chlorine           Potassium    Iodine 

           Iodide                                          Chloride

    iv). 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

        a). 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:

    • ZnSO4 (aq)    +   BaCl2 (aq)     →   ZnCl2 (aq)   +  BaSO4 (s) 

             Zinc                  Barium                 Zinc                Barium     

          Sulphate             Chloride              Chloride        Sulphate (White)

    • 2 HCl (aq)      +   Pb(NO3)2(aq) →  2 HNO3 (aq)  +  PbCl2 (s) ↓ 

            Hydrochloric     Lead                        Nitric              Lead  (White) 

           Acid                        Nitrate                    Acid                Chloride

    • Pb(NO3)2(aq)  +   2 KI (aq)        →    PbI2 (aq)  ↓ +   KNO3 (s)     

             Lead                       Potassium          lead                  Potassium     

             Nitrate                    Iodide                 Iodide              Nitrate

     

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

    • NaOH (aq)   +  HCl (aq)       →      NaCl (aq)     +    H2O

            Sodium          Hydrochloric       Sodium             Water

           Hydroxide      Acid                        Chloride

           (Base)             (Acid)                      (Salt)                (Water)

    • ZnO     +     HNO3    →   Zn(NO3)2   +   H2O

             Zinc            Nitric           Zinc                 Water

             Oxide         Acid             Nitrate

    All these types of Combination, Decomposition, Displacement and Double Displacement reactions are explained using examples along with the colour change that takes place during reactions.

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