Chemical reaction and equation notes class 10 science (Part - 2)

Types of chemical reaction

1.     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

2.     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:

a)    Thermal Decomposition

FeSO4 Fe2O3 + SO2 + SO3

Pb(NO3)2 PbO + NO2 + O2

KClO3 KCl +O2

b)    Electric Decomposition

H2O H2 + O2

NaCl Na + Cl2

Al2O3 Al + O2

c)     Decomposition by light

AgCl Ag + Cl2

AgBr Ag + Br2

These reactions are used in black & white photography

3.     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

4.     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

5.     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

Example:

OXIDATION PROCESS

CuO + H2 Cu + H2O

REDDUCTION PROCESS

·       Oxidising Agent = CuO

·       Reducing Agent = H2

·       Oxidised Substance = H2

·       Reduced substance = CuO

b)     OXIDATION PROCESS

H2S + Cl2 S + HCl

REDUCTION PROCESS

·       Oxidising Agent = Cl2

·       Reducing Agent = H2S

·       Oxidized substance = H2S

·       Reduced substance = Cl2

Substance present at tail of reduction is called the Oxidising agent

Effects of Oxidation

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

a)   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

b)  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 anti oxidants 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