CHAPTER NO 2

CHAPTER NO 2
CHEMICAL REACTIONS & CHEMICAL EQUATIONS 

 TYPES OF CHEMICAL REACTIONS

   There are six types of chemical reactions:

ADDITION REACTION (SYNTHESIS).

DECOMPOSITION.

DISPLACEMENT.

DOUBLE DISPLACEMENT.

NEUTRALIZATION.

HYDROLYSIS

ADDITION REACTIONS OR SYNTHESIS

Chemical reactions in which two or more substances react to produce one compound are known as    addition reaction.

   They can be represented as:

A + B è AB

   EXAMPLE:

H2 + Cl2 è 2HCl

SO2 + Cl2 è SO2Cl2

DECOMPOSITION

 A chemical reaction in which a compound splits into two or more fragment is called decomposition.

   They can be represented as:

AB è A+B

   EXAMPLE:

2KClO3 + HEAT è 2KCl + 3O2

CH4 + HEAT è C + 2H2

   Usually for decomposition heat is required.

DISPLACEMENT REACTION

   A chemical reaction in which a radical or group replaces another radical or group form a compound and    takes its position is called a displacement reaction.

   They can be represented as:

A + BC è AC + B

EXAMPLE:

Zn + H2SO4 è ZnSO4 + H2

Zn + CuSO4 è ZnSO4 + Cu

DOUBLE DISPLACEMENT

 A chemical reaction in which two substances are decomposed to form new substances by exchanging their    radicals is called double displacement reaction.

   They can be represented as:

AB+CD è AD+CB

   EXAMPLE:

BaCl2 + Na2SO4 è BaSO4 + 2NaCl

AgNO3+ NaCl è AgCl + NaNO3

NEUTRALIZATION

   A chemical reaction in which an acid and a base react to form salt and water is called Neutralization.

Acid + Base è Salt + Water

EXAMPLE:

HCl + NaOH è NaCl + H2O

HNO3 + NaOH è NaNO3 + H2O

HYDROLYSIS

The type of double displacement reaction in which one reactant is water is called "Hydrolysis".

OR

Reaction of a substance with water in which PH of water is changed is referred to as "Hydrolysis".

   EXAMPLE:

FeCl3 + 3H2O è Fe (OH)3 + 3HCl

Na2CO3+2H2O è 2NaOH+ H2CO3

ENDOTHERMIC REACATION-EXCOTHERMIC REACTIONS-LAW 

OF CONSERVATION OF MASS

 ENDOTHERMIC REACTION

"All those chemical reaction in which heat is absorbed in going

from reactants to product are known as "Endothermic reactions."

   These reactions can not proceed without addition of heat.

   For example

2KClO3 + Heat è 2KCl + 3O2

CaCO3 + Heat è CaO + CO2

Graphical Representation

EXOTHERMIC REACTION

   All those chemical in which heat is released in going from reactant to product are known as exothermic    reactions.

   For example

3H2 + N2 è 2NH3 + Heat

2SO2+O2 è 2SO3 + Heat

Graphical Representation

 

CHEMICAL REACTION

   A process in which chemical change in the nature and composition of substances occurs is called chemical    reaction

   For example

CaCO3 + HEATè CO2 + CaO

3H2 + N2 è 2NH3

CHEMICAL EQUATION

   A chemical equation is a symbolic formation of chemical change in terms of symbols and formula.

CHARACTERISTICS OF A CHEMICAL EQUATION

   1. A chemical equation must be a representative of a chemical reaction.

   2. It should represent molar quantities.

   3. It should be balanced in terms of atoms and molecules of reactants and products.

   For example:

2SO2+O2 è 2SO3

3H2 + N2 è 2NH3

LAW OF CONVERSATION OF MASS

   The law of conservation of mass indicates that during any process, mass is neither created nor destroyed.

   The law was put forward by a French chemist LAVOISER in 1785.

   Law of conversation of mass states that :

Mass can neither be created nor destroyed during a chemical reaction.

During a chemical reaction total mass of products is equal to the total mass of reactant