CHEMICAL REACTIONS AND EQUATIONS

Writing a Chemical Reaction

Types of Chemical Reaction

Oxidation & Reduction

There are two types of reactions 

(I) CHEMICAL REACTION  (II) PHYSICAL REACTION

CHEMICAL REACTION: In a reaction when the original state of the particle changes 

and it cannot be reversed by simple physical means, this type of reaction is known 

as chemical reaction. Example :- Fermentation of grapes, burning of wood etc. In 

this reaction we have seen that after burning of wood, coal is formed and we cannot 

make wood from coal. 

 PHYSICAL REACTION: In a reaction when original state of the particle can be 

recovered by any means then this type of reaction is known as physical reaction. 

Example :- Evaporation of water is the example of physical reaction because we can 

turn vapour into water again

 WRITING A CHEMICAL RECTION

 When we are going to write a chemical equation then there will be reactant and 

product. Left hand side of the equation is called reactant and the right hand side of 

the equation is called product.

2H2+ O2 = 2H20

Reactant             Product

• Balanced Chemical Equations

According to the Law of conservation of energy we know that energy can neither be 

created nor destroyed. So while writing a chemical equations we should keep in mind 

that number of atoms in L.H.S and R.H.S of an equation should me balanced.

 TYPES OF CHEMICAL REACTION

COMBINATION REACTION :-In a combination reaction two or more substances 

combine to form a new single substance.

DECOMPOSITION REACTION :-- Decomposition reactions are opposite to 

combination reactions. In a decomposition reaction, a single substance decomposes 

to give two or more substances.

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Example: CaO + H2O = Ca(OH)2

 Quick Lime                              Slaked Lime

 2H2 + O2 = 2H2O

 Hydrogen Oxygen Water 

DISPALCEMENT REACTION :- When an element displaces another element from 

its compound, a displacement reaction occurs.

DOUBLE DISPLACEMENT REACTION :-- Two different atoms or groups of atoms 

(ions) are exchanged in double displacement reactions.

EXOTHERMIC REACTION :-- Reaction in which heat generated is called exothermic 

reaction.

ENDOTHERMIC REACTION :-- Reaction in which energy is absorbed is known as 

endothermic reaction.

Oxidation and Reduction

OXIDATION :-- Oxidation is the gain of oxygen or loss of hydrogen.

If a substance gains oxygen during a reaction, it is said to be oxidized.

REDUCTION :-- Reduction is the loss of oxygen or gain of hydrogen.

If a substance loses oxygen during a reaction it is said to be reduced.

Corrosion

We must have observed that iron particles are shiny when new, but get coated with a 

reddish brown powder when left for some time. This process is commonly known as 

rusting of iron. 

When a metal is attacked by substances around it such as moisture, acids, etc., it is 

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Example: 2Cu + O2 = 2CuO

 Copper is getting oxidised

 CuO + H2 = Cu + H2O

 Copper Oxide is reduced

Example: Na2SO4 + BaCl2 = BaSO4 + 2NaCl

 Sodium Sulphate + Barium Chloride = Barium Sulphate + Sodium Chloride

Example : Fe + CuSO4 = FeSO4 + Cu

 Copper Sulphate Iron Sulphate

Example: 2Fe SO4 = Fe2O3 + SO2 + SO3

 Ferrous Sulphate Ferric OxideFinish Line & Beyond

said to corrode and this process is called corrosion.

Corrosion is harmful for many things, like car body, electric poles,etc. To prevent 

corrosion most of the things made of metal are given a thick coat of paint.

Example :- The black coating on silver and the green coating on copper are common 

examples of corrosion.