Chemical reaction and equation

Chemical reaction and equation Part 2

Types of chemical reaction on the basis of heat

Endothermic reaction

Those chemical reactions in which heat is absorbed to complete the reaction are called endothermic reaction.

  • CaCO3                    CaO + CO2
  • Pb(NO3)2                  PbO + NO2 + O2
  • FeSO4              Fe2O3 + SO2 + SO3 

Exothermic reaction

That chemical reaction in which heat is released along with the product is called exothermic reaction.

  • CaO + H2O           Ca(OH)2
  • C +O2              CO2
  • Mg +O2                  MgO
  • CH4 +O2             CO2 + H2O

NOTE: C6H12O6 + O2             CO2 + H2O + Energy (Respiration is also on endothermic reaction)

Types of chemical reaction

Combination Reactions

Those reactions in which two or more than two substances combine to form a single product are called combination reactions such as:

  • H2 + O2                    H2O
  • NH3 + HCl            NH4Cl

Decomposition Reaction

Those reactions in which a compound splits up into two or more than two substances are called decomposition reactions. The process of decomposition may takes place in three forms:

  1. Thermal Decomposition

FeSO4              Fe2O3 + SO2 + SO3

Pb(NO3)2                  PbO + NO2 + O2

KClO3                        KCl +O2

  • Electric Decomposition

H2O              H2 + O2

NaCl              Na + Cl2

Al2O3                    Al + O2

  • Decomposition by light

AgCl             Ag + Cl2

AgBr             Ag + Br2

These reactions are used in black & white photography

Displacement Reaction

Those reactions in which one element takes the place of another element in a compound are called single displacement reactions such as:

CuSO4 + Zn                ZnSO4 + Cu

CuSO4 + Fe                FeSO4 + Cu

CuCl2 + Pb                 PbCl2 + Cu

Na + H2O                  NaOH + H2

CuO + Mg                MgO + Cu

Double Displacement Reaction

Those reactions in which two compounds react by an exchange of long to form two new compounds are called double displacement reaction.

BaCl2 + CuSO4           BaSO4 + CuCl2

CuSO4 + H2S               CuS + H2SO4

AlCl3   + NH4OH             Al(OH)3  + NH4Cl

Redox Reaction

Those reactions in which both oxidation and reduction take place are called Redox reaction.

Oxidation:  Addition of oxygen/Removal of Hydrogen

Reduction: Addition of Hydrogen/Removal of Oxygen

Effects of Oxidation

Two common effects of oxidant action are corrosions of metals & rancidity of food

Corrosion

Process in which metals are eaten up gradually by action of air moisture or a chemical on their surface are called corrosion.

    • Corrosion of iron is called rusting of iron
    • Corrosion of other metals called corrode Fe + O2 + H2O             Fe2O3 + H2O                                         

    Rancidity

    The condition in which our food becomes spoils due to Arial oxidation of food and marked by unpleasant smell.

    Prevention method

    Rancidity can be prevented by the adding of antioxidants to food containing fats and oils.

    • we use BHA (Butylated Hydroxy anisole) & BHT (Butylated hydroxyl toluene) as antioxidant
    • Rancidity can be prevented by  packaging food in  nitrogen gas
    • Rancidity can be prevented by  storing food in  air tight containers
    • Rancidity can be prevented by keeping the food in a refrigerator
    • By placing food away from sun light
    Click here For part 1

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