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• Chemical Reaction:  It is a process in which reactants reacts to form products.
      Zn     +        H₂SO₄          →         ZnSO₄         +        H₂
   (Zinc)         (Sulphuric acid)          (Zinc Sulphate)       (Hydrogen)
             [Reactants]                                            [Products]

• Chemical Equation:
  • A symbolic representation of chemical reaction in form of formula or symbol.
                                                                                       Direction of Reaction
        2H_2(g)       +      O_2(g)                       →                     2H₂O_(g)
     (Hydrogen)         (Oxygen)                                                   (Water)
    [Reactant on Left Side]                                         [Product on Right Side]
  • Physical states of compounds are indicated by:
    

    State	Denoted by
    Gaseous State	(g)
    Liquid State	(l)
    Solid State	(s)
    Aqueous State	(aq)
    Precipitate	↓

• Skeletal Chemical Equation:  A chemical equation which represents reaction in terms of formula and symbols.
           Mg            +          O₂         →        MgO
   (Magnesium)         (Oxygen)                (Magnesium Oxide)
• Balanced Chemical Equation:  A chemical equation in which number of atoms of element on reactant side is equal to number of atoms in product side.
       2Mg     +      O₂          →            2MgO
  Atoms of Reactant Side = Atoms of Product Side
          [Mg=2, O=2]                            [Mg=2, O=2]
  • Steps for balancing chemical equation:
    1. Unbalanced equation:
            Mg     +      O₂          →        MgO
    2. Start balancing with compound containing maximum number of atoms.
            Mg     +      O₂          →        2MgO
    3. Balance untill atoms of elements in reactant, becomes equal to atoms of elements in product.
            2Mg     +      O₂          →        2MgO
    4. Provide with physical state.
            2Mg_(s)     +      O_2(g)          →        2MgO_(s)
    5. Indicate reaction condition above or below the arrow.
• Types of Chemical Reaction:
  1. Combination reaction:  Two or more reactants combines to form single product.
         C_(s)         +         O_2(g)          →        CO_2(g)
      (Carbon)         (Oxygen)                      (Carbon Dioxide)
               [Reactants]                               [Single Product]

  2. Exothermic Reaction:  Heat is evolved during reaction.  e.g.  Burning of Natural Gas is exothermic reaction.
         CH_4(g)      +      2O_2(g)          →             CO_2(g)              +       2H₂O_(g)
      (Methane)            (Oxygen)                   (Carbon Dioxide)                (Water)

  3. Decomposition Reaction:  Single substance decomposes to form two or more products.
                                                                 Heat
         2FeSO_4(s)                →           Fe₂O_3(s)        +          SO_2(g)            +          SO_3(g)
     (Ferrous Sulfate)                         (Ferric Oxide)          (Sulfur Dioxide)        (Sulfur Trioxide)
     [Single Substance]                                           [Two or more products]

  4. Thermal Decomposition Reaction:  Decomposition reaction carried out in presence of heat.
                                                      Heat
         CaCO_3(s)          →           CaO_(s)        +          CO_2(g)
       (Limestone)                         (Quicklime)          (Carbon Dioxide)

  5. Endothermic Reaction:  Heat is absorbed during reaction.
                                                        Sunlight
           2AgCl_(s)             →           2Ag_(s)        +        Cl_2(g)
     (Silver Chloride)                         (Silver)              (Chlorine Gas)

  6. Displacement Reaction:  One element displaces another element from its compound.
       Fe_(s)     +       CuSO_4(aq)            →             FeSO_4(aq)       +       Cu_(s)
      (Iron)           (Copper Sulphate)                    (Iron Sulphate)             (Copper)

  7. Double Displacement Reaction:  Two different atoms or groups of atoms are exchanged during the reaction.
           Na₂SO_4(aq)         +         BaCl_2(aq)                →          BaSO_4(s)              +          2NaCl_(aq)
     (Sodium Sulphate)           (Barium Chloride)                    (Barium Sulphate)             (Sodium Chloride)

  8. Precipitation Reaction:  Reaction involving formation of precipitate.
           Na₂SO_4(aq)         +         BaCl_2(aq)                →         BaSO_4(s)   ↓          +          2NaCl_(aq)
     (Sodium Sulphate)           (Barium Chloride)                    (Barium Sulphate)             (Sodium Chloride)

  9. Oxidation Reaction:  Gain of Oxygen or Loss of Hydrogen.
                                                                            Heat
         2Cu       +         O₂          →          2CuO
      (Copper)        (Oxygen)                (Copper Oxide)

  10. Reduction Reaction:  Gain of Hydrogen or Loss of Oxygen.
                 CuO           +           H₂             →          Cu          +       H₂O
       (Copper Oxide)        (Hydrogen)                   (Copper)             (Water)

  11. Redox Reaction:  Oxidation and reduction occur simultaneously, where, one reactant get oxidised while other reactant get reduced.
      
      
• Effects of oxidation:
  1. Corrosion:  Rusting of metals due to corrosive substances (moisture in air, acids, etc). It can be prevented by painting metal surfaces.
  2. Rancidity:  Oxidation of fats and oils that changes their taste and smell. It can be prevented by adding antioxidants to substance containing oils and fats.