Chapter 1 Chemical Reaction and Equation (class10)

1 Chemical Reaction :  During chemical  reaction, chemical composition of substances changes or new substances are formed.

2. Chemical Equation: Chemical reactions can be written in chemical equation form which should always balanced .

3. Types of Chemical Reaction
   (1) Combination reaction: A single product is formed from two or more reactants.
                                        2 Mg + O2 -> 2 MgO

   (2) Decomposition reaction : A single product breaks down to yield two or more products:

1. Thermal decomposition :   PB(NO₃)₂ = 2 PBO + 4 NO₂ + O2
2. Electrolysis  : 2H2 + O2 = 2H2O
3. Photochemical reaction : 2AgBr(s)+ Sunlight → 2Ag(s) + Br2(g)

(3) Displacement reaction : one element is displaced by another element.

                                Fe + CuSO₄ → FeSO₄ + Cu 

(4) Double displacement reaction : Exchange of ions between reactants.

                                  AB + CD → AD + CB

                           AgNO₃ + NaCl → AgCl + NaNO₃

(5)Redox reaction : Both oxidation and reduction take place simultaneously.

                                 Cuo + H2 ------ Cu + H2O

(6) Exothermic reaction: A chemical reaction in which heat energy is evolved.

                                 C+ O2 = CO2 ( heat)

(7) Endothermic reaction: A chemical reaction in which heat energy  is absorbed .

                               ZnCO3+ Heat =  ZnO + CO2

(8) Redox reaction : chemical reaction in which both oxidation and reduction take place simultaneously.

(9) Oxidation: reaction that involves the gain of oxygen or loss of hydrogen .

(10) Reduction: Reaction that shows the loss of oxygen or gain of hydrogen.

                         ZnO+ C = Zn+ CO

    ( ZnO is reduced to Zn,  C is oxidized to CO - oxidation)

(4) Corrosion : It is an undesirable change that occurs in metals , when they are attacked by moisture, air, acids and bases.

    Example: Corrosion( Rusting Of iron) : Fe2O3.n H2O (hydrated iron oxide)

               Corrosion of Sliver: Ag2S (Sliver Sulphide)

               Corrosion Of Aluminium :  Al2O3 ( Aluminum Oxide)

(5) Rancidity: Undersirable change that takes palce in oil containing food items due to the oxidation of fatty acids.

  Prevention methods of rancidity : Adding antioxidants to the food materials storing food in air tight container ,flushing out air with nitrogen gas and refrigerator.