Different Chemical Reactions & Balancing

Equations
CHEMICAL REACTION
• Chemical Reactions are associated with
chemical change.
• Whenever a chemical change occurs chemical
reaction is said to take place.
• Chemical Reactions are usually irreversible and a
new product is formed.
Signs of Chemical Reactions

There are five main signs that indicate a chemical reaction

has taken place:
 Change in colour
 Production of an odor
 Change in temperature
 Evolution of a gas
 Precipitate formation
Types of Chemical Reactions
1.Combination reaction A+BAB
2. Decomposition reaction ABA+B
3.Single displacement reaction
A+BCACB
4.Double –displacement reaction
AB+CDAD+B
5.Redox reaction
 Combination Reactions
 These type of reactions occur when two reactants combine to form one
or more products E.g.-
1. CaO + H2O Ca(OH)2
2. C + O2 CO2

 They are generally exothermic reactions which

involve evolution of heat during reaction
 Combination reaction

2Na + Cl2 2NaCl

Na Cl 
Cl
Na

General Form:-
A + B AB
element or element or compound
compound compound
 Decomposition reaction
The type s of reaction in which a single reactant breaks
down to give simpler products are called decomposition
reaction.
E.g.- 2H2O 2H2 + O2

When a decomposition reaction is carried out by heating ,

it is known as thermal decomposition.
 Decomposition Reaction
 Decomposition Reaction

2H20 2H2 + O2

0
H +

H

General form : AB A + B
compound two or more elements
or compounds
Decomposition reaction

 Hydrogen peroxide
2H2O 2H20 + O2
 Electrolysis of water
2H2O 2H2 + O2
 Nitrogen trioxide
2Nl3 N2 + 3l2
 General form
AB A + B
Displacement reactions

This reaction in which a more reactive

element displaces a less reactive element
from its solution is known as displacement
reaction
They are of two types:
1. Single displacement reaction
2.Double displacement reaction
 1. Single Displacement Reactions

Single- replacement reaction

Mg + CuSO4 MgSO4 + Cu

General form:
A + BC AC + B
 Single Displacement Reaction

Lead(II) chloride + potassium iodide potassium chloride + Lead(II)iodide

Pb2+ Cl1- K1+ l1- Pb2+ Cl1- K+ I1-

PbCl2 + Kl KCl(aq) + Pbl2(ppt)

 2.Double Displacement reaction

CaCo3 + 2HCl CaCl2 + H2C03

General form :
AB+CDAD+CB

K2CO2(aq) +BaCl2(aq) 2KCl + BaCo3(s)

Reactivity series
Potassium
more reactive k

Sodium Na
Calcium Ca
Magnesium Mg
Aluminium Al
Carbon C
Zinc Fe
Iron Zn
Tin Sn
Lead Pb
Hydrogen H
Copper Cu
Silver Ag
Gold Au
Platinium Pt
least reactive
Redox reactions

 If a substance gains oxygen during a reaction it is said to

be oxidised
 If a substance loses oxygen during a reaction it is said to
be reduced
 Reactions in which this type of change occurs is known
as oxidation and reduction reactions or redox reactions
 Eg:CuO+H2Cu+H2O
CHEMICAL EQUATIONS

The simplest form of description of a chemical reaction in a shorter form is by

writing it in the form of an equation. E.g.-

Mg + O2 MgO

 The reactants are written on the left side and product is written on the right
side.
 An arrow is placed between them to show the direction of reaction.
SYMBOL USED IN CHEMICAL EQUATION
SYMBOLS MEANING

• Used to separate one reactant or product from

+
one another.
• Can be read “reacts with” when used in reactant,
read as “and” when it is used in product.

• Used to separate the reactants from the products.

• Read as “yields” or “produces” in an equation.

• Indicates that there is heat applied or needed to

make the reaction proceed.
(s) • Indicates that the substance is in the
solid state.

(l) • Indicates that the substance is in the

liquid state.

(g) • Indicates that the substance is in the

gas state.

• Indicates that the substance is

(aq) dissolved I water.
• Comes from the term “aqueous”.
Showing Phases in Chemical Equations

H2O(s) H2O(l) H2O(g)

Solid Phase-the substance is relatively rigid and has a definite volume and
shape. Ex.-NaCl(s)
Liquid Phase-the substance has a definite volume, but is able to change
shape by flowing. Ex.-H2O(l)
Gaseous Phase-the substance has no definite volume or shape, and it shws
little response to gravity. Ex.-Cl2
Word Equations

A Word Equation describes chemical change using the names of the

reactants and products.

Write the word equation for the reaction of methane gas with oxygen gas to
form carbon dioxide and water.
Methane + oxygen carbon dioxide + water

Reactant Product

CH4 + 2O2 CO2 + 2H2O

Balanced Chemical Equations

 According to the law of conservation of mass, total mass must be equal on

the both sides of the equation.
 This type of equation is known as a Balanced Chemical Reaction. E.g.-

2Mg + O2 2MgO

 Here both sides have two atoms of Magnesium and two atoms of Oxygen.
STEPS IN BALANCING CHEMICAL
EQUATIONS
1.Check for diatomic molecules :- These are molecules composed of only two
atoms, of either the same or different chemical elements.
This includes H2, O2, N2, Cl2, Br2, F2, and I2.
2.Check whether the chemical formulas of all the reactants
and products are correct. Check the total number of
atoms of each element on each side of the equation.
3.A polyatomic ion appearing unchanged on both sides of
the equation is counted as a single unit.
4.Balance the elements one at a time by using coefficients.
Must no attempt to the balance the equation by changing
the subscripts in the chemical formula of a substance.
5.Check each atom or polyatomic ion to be sure that the
equation is balanced.
PRESENTED BY:

PRIYANKA SAHU(210804130014)
SOURAV MEHER(210804130015)
SANDEEP KUMAR SINGHA(210804130044)
KADIMCHERLA NAGA VISHNAVI(210804130045)
THANK YOU