CHAPTER-1: CHEMICAL REACTION AND EQUATIONS (NOTES CBSE CLASS 10 )

Chapter 1

CHEMICAL REACTION AND EQUATIONS

Chemical equation 

• a chemical equation represent a chemical reaction
• In a chemical equation the number of atom of each element of the reactant side( left hand side ) must be equal to the number of atoms at product side (right hand side)

Balanced chemical equation 

If the number of atom of each element on the reactant and the product side are same on both side of the equation then equation is said to be balanced chemical equation

Example

Zn + H2SO4 -------------------->  ZnSO4 + H2

	Reactant side	product side
number of zinc atoms	1	1
Number of hydrogen atoms	2	2
number of Sulphur atoms	1	1
number of oxygen atoms	4	4

Unbalanced chemical equation

• When the number of atom of each element does not same on the both side then chemical equation is said to be unbalanced chemical equation

Example

Mg+O2----------->MgO(Unbalanced)

2Mg+O2----------->2MgO(balanced)

Note:- to make a chemical  equation more informative the physical states of the reactants and products are mentioned along with their chemical formula the gaseous, liquid and solid states of reactants and products are represented by the notation (g) (l) (aq) and (s) Respectively.

Example

3Fe(S)+4H2O(g) ------------------> Fe3O4(s)+4H2(g)

TYPES OF CHEMICAL EQUATIONS

1.Combination reaction

A Reaction in which a single product is formed from two or more reactants is known as a combination reaction

Example

CaO(s)+H2O(l)------------->Ca(OH)2(aq)

2.Exothermic reaction

Reaction in which heat is released along with the formation of products are called  Exothermic chemical reaction

Example

C6H12O6(aq)+6O2(g)+6H2O(l)------------>6CO2(aq)+12H2O(l)+energy

3.Decomposition reaction 

when a reactant is broke down into several compound (products) or we can say more than one product such  type of reaction is known as decomposition reaction 

1. CaCO3(s)------------>CaO(s)+CO2(g)
2. 2Pb(NO3)2(s)------->2PbO(s)+4NO2(g)+O2(g)
3. 2AgCl(s)------------->2Ag(s)+Cl2(g)
4. 2AgBr(s)------------->2Ag(s)+Br2(g)
5. 2FeSO4(s)------------>Fe3O3(s)+SO2(g)+SO3(g)

4.Endothermic reaction 

Reaction in which energy is absorbed at reactant side are known as endothermic reaction

Note :-decomposition reaction required energy in the form of heat light or electricity for Breaking Down The reactant

5.Double displacement reaction

The reaction in which there is exchange of ions between the reactants are called double displacement reaction

Example

Na2SO4(aq)+BaCl2(aq)-------------->BaSO4(s)+NaCl(s)

6.Oxidation and reduction reaction

• If a substance gain oxygen and loses hydrogen during the reaction it is said to be oxidised (oxidation)
• If a substance gain hydrogen and lose oxygen during the reaction it is said to be reduced(reduction)

7.Redox Reaction

The reaction in which one reactant get oxidized while the other get reduced during the reaction such a reaction are oxidation reduction or Redox reaction 

Example

CuO+H2------------->Cu+H2O

Corrosion 

When a metal is attacked by a substance around it such as moisture, acid etc it is said to be corroded and this process is called corrosion

• Rusting of iron:- iron articles are Shiny when new but get coated with the reddish Brown powder when left in Presence of air and moisture
• Black coating of silver
• Green coating on copper

Rancidity

When fats and oils are oxidized they become ranacid and their smells and taste change

• To prevent fat and oil from the oxidation we use antioxidant
• to slow down the oxidation process We keep food in air tight containers
• some manufacturer use inert gas to prevent food item from oxidation examples :chips packet