Chemical Reactions And
Equations
Make chemistry easy
Types of Change
chemical change Physical change
A change in which A change in which only the
a new substance is shape, size, or state of a
formed with substance changes and no
different properties new substance is formed
(Example: rusting of iron). (Example: melting of ice).
Chemical Reactions
The transformation of chemical substance into another chemical. substance. e.g. Rusting of
iron, the setting of milk into curd.
Chemical Equations
Representation of chemical reaction using symbols and formulae of the substances
A+B
A+B
Reactants
C+D
C+D
Product
Example :- Mg+O2 MgO
Characteristics of chemical reactions
1. change in colour
2.change in temperature
a) exothermic reaction
b) endothermic reaction
3.change in state
4.formation of precipitate
Important key terms
Precipitate : is the insoluble solid which settles down after the completion of the chemical reaction.
Exothermic reactions: The chemical reactions that release heat energy.
Endothermic reactions : The chemical reactions in which heat energy is absorbed.
Catalyst : A catalyst is a substance that speeds up a chemical reaction, or lowers the temperature or pressure
needed to start one, without itself being consumed during the reaction.
, Representing Chemical Reactions
A skeletal equation is an unbalanced equation. In a skeletal equation equation the number of atoms on reactant side are not
equal to product side.
A chemical equation in which the number of atoms of each element on reactant side is equal to that of product side is called
balanced chemical equation. Balancing of chemical equation is done to follow the law of conservation of mass('mass can
neither be created nor be destroyed during a chemical reaction').
The method used for balancing chemical equations is called hit and trial method(i.e. Jugaad) as we make trials to balance the
equation by using the smallest whole number coefficient.
Example:- Balance:- Fe +H2O Fe3O4 + H2
Step 1: Check the number of atoms of each element on the reactants and products side of the equation
No. of atoms in No. of atoms in
Elements
Reactants Side Product Side
FE 1 3
H 2 2
O 1 4
Step 2: First of all, to balance oxygen atoms we multiply H20 molecules by 4
Fe + 4(H2O) Fe3O4 + H2
Step 3:- Once again check the number of atoms of each element on both sides
No. of atoms in No. of atoms in
Elements
Reactants Side Product Side
FE 1 3
H 8 2
O 4 4
Step 4: Balancing Hydrogen atom by multiplying H2 with 4 (since, 4H2 8 atoms) Fe +
4(H2O) Fe304 + 4(H2)
Now,
No. of atoms in No. of atoms in
Elements
Reactants Side Product Side
FE 1 3
H 8 8
O 4 4
Step 5: Balancing Fe by multiplying by 3 on LHS
3(Fe) +4(H2O) Fe3O4 + 4(H2)
We can see,
Equations
Make chemistry easy
Types of Change
chemical change Physical change
A change in which A change in which only the
a new substance is shape, size, or state of a
formed with substance changes and no
different properties new substance is formed
(Example: rusting of iron). (Example: melting of ice).
Chemical Reactions
The transformation of chemical substance into another chemical. substance. e.g. Rusting of
iron, the setting of milk into curd.
Chemical Equations
Representation of chemical reaction using symbols and formulae of the substances
A+B
A+B
Reactants
C+D
C+D
Product
Example :- Mg+O2 MgO
Characteristics of chemical reactions
1. change in colour
2.change in temperature
a) exothermic reaction
b) endothermic reaction
3.change in state
4.formation of precipitate
Important key terms
Precipitate : is the insoluble solid which settles down after the completion of the chemical reaction.
Exothermic reactions: The chemical reactions that release heat energy.
Endothermic reactions : The chemical reactions in which heat energy is absorbed.
Catalyst : A catalyst is a substance that speeds up a chemical reaction, or lowers the temperature or pressure
needed to start one, without itself being consumed during the reaction.
, Representing Chemical Reactions
A skeletal equation is an unbalanced equation. In a skeletal equation equation the number of atoms on reactant side are not
equal to product side.
A chemical equation in which the number of atoms of each element on reactant side is equal to that of product side is called
balanced chemical equation. Balancing of chemical equation is done to follow the law of conservation of mass('mass can
neither be created nor be destroyed during a chemical reaction').
The method used for balancing chemical equations is called hit and trial method(i.e. Jugaad) as we make trials to balance the
equation by using the smallest whole number coefficient.
Example:- Balance:- Fe +H2O Fe3O4 + H2
Step 1: Check the number of atoms of each element on the reactants and products side of the equation
No. of atoms in No. of atoms in
Elements
Reactants Side Product Side
FE 1 3
H 2 2
O 1 4
Step 2: First of all, to balance oxygen atoms we multiply H20 molecules by 4
Fe + 4(H2O) Fe3O4 + H2
Step 3:- Once again check the number of atoms of each element on both sides
No. of atoms in No. of atoms in
Elements
Reactants Side Product Side
FE 1 3
H 8 2
O 4 4
Step 4: Balancing Hydrogen atom by multiplying H2 with 4 (since, 4H2 8 atoms) Fe +
4(H2O) Fe304 + 4(H2)
Now,
No. of atoms in No. of atoms in
Elements
Reactants Side Product Side
FE 1 3
H 8 8
O 4 4
Step 5: Balancing Fe by multiplying by 3 on LHS
3(Fe) +4(H2O) Fe3O4 + 4(H2)
We can see,
