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Calassify the chemical reactions into varous types depending on the way the products are formed by giving suitable examples. |
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Answer» Solution : (i)Chemical combination : Thereaction in which two substances , that is , ELEMENTS , compounds or both combine to form a new compound is called chemicalcombination. Representation :`X+YtoXY` `{:("Type","Example"),("Element - element (synthesis)",H_(2)+Cl_(2)to2HCl),("Element - compound",2SO_(2)+O_(2)to2SO_(3)),("Compound - compound",CaO+H_(2)OtoCa(OH)_(2)):}` (ii) Chemical decomposition :The reaction in which a compound undergoes decomposition to form more than one substance in the PRESENCE of heat or light or electricity is called chemical decomposition. Representation :`ABtoA+B` `{:("Type","Example"),("Thermal decomposition (In presence of heat)",2Pb(NO_(3))_(2)to2PbO+4NO_(2)+O_(2)),("Photolytic decomposition (In presence of light)",2HOCl to2HCl+O_(2)),("Electrolytic decomposition (By passing electricity)",2H_(2)Oto2H_(2)+O_(2)):}` (iii)Chemical displacement :When few pieces of zinc are dipped ingreen coloured ferrous SULPHATE solution , the COLOUR disappears after some time and ironis found to be deposited .Thisphennomenon takes place because zinc is more active metal than iron and hence it takes away the other constituent that is iron from ferrous sulphate and iron gets separated. Whereas , when copper is added to the ferrous sulphate solution , no change is observed . from this observation it can be concluded that copper is less active metal than iron. The chemical reaction in which the more REACTIVE element displaces the less reactive element from its compound is called chemical displacement reaction. Representation : `X+YZtoXZ+Y` X is more reactive element than Y. `Y+XZto` Noreaction Y cannot displace X from its compound since it is less reactive than X. Example :`Zn+FeSO_(4)toZnSO_(4)+Fe` `Cu+FeSO_(4)to` no reaction (iv)Chemical double decomposition / double displacement : The chemical reaction in which the two reactant (compounds) exchange their respective radicals and two other new compounds are formed is called double displacement reaction. Representation : `AB+XYtoAY+XB` Where B and Ycorrespond to the negative radicals which are exchanged to give AY and XB. Example :`2KNO_(3)+FeSO_(4)toK_(2)SO_(4)+Fe(NO_(3))_(2)` In the above reactive `K^(+)` (potassium ion) combines with `SO^(4-)` (sulphate ion) and `Fe^(+2)` (ferrous ion) combines with `NO^(3-)` (nitrate ion) to form two new compounds , `K_(2)SO_(4) and Fe(NO_(3))_(2)` . During certain double displacement reactions , a solid substance is found to be deposited . The solid deposition is called precipitate and this of reaction is called precipitation reaction. Example :`NaCl+AgNO_(3)toNaNO_(3)+AgCl` in theabove reaction , during the exchange of radicals , silver chloride is formed which is insoluble in water . therefore it remains as a solid at the bottom of the container as precipitate. |
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