class 9

1. Done by-
Debjani
Purkayastha

2.  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.

3.  There are five main signs that indicate a chemical
reaction has taken place:
 change in color
 Evolution of a gas
 Change in temperature
 Change in state

4.  The equation must represent known facts.
 The equation must contain the correct formulas for
the reactants and products.
 The law of conservation of mass must be satisfied.
 lets watch this video:
https://www.youtube.com/watch?v=8w9yRxBZzSo

5.  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 + CB
 Lets watch this video:-
https://www.youtube.com/watch?v=WWJQpuv9ElE

6. 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 CO
They are generally exothermic reactions which involve
evolution of heat during reaction.

7.  2 Na + Cl2  2 NaCl
 General form:
A + B  AB
 element or compound element or compound  compound

8.  The types of reaction in which a single reactant
breaks down to give simpler products are called
decomposition reaction.
E.g.-
2 H2O  2 H2 + O2
 When a decomposition reaction is carried out by
heating, it is known as thermal decomposition.

9.  2H2O  2 H2 + O2
 General form:
AB  A + B
compound two or more elements or compounds

10.  Hydrogen Peroxide
H2O2  H2O + O2
 Electrolysis of water
2H2O  2H2 + O2
 Nitrogen tri-iodide
2NI3  N2 + 3 I2

11.  The 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

12.  Mg + CuSO4  MgSO4 + Cu
 General form:
 A + BC  AC + B
 Eg:-
lead (II) chloride + potassium iodide  potassium chloride + lead (II) iodide
PbCl2 + KI  KCl + PbI2

13.  CaCO3 + 2 HCl  CaCl2 + H2CO3
 General form:
AB + CD  AD + CB

15. Photochemical reaction, Electrochemical reaction
Photochemical reaction, a
chemical reaction initiated by the
absorption of energy in the form of
light. The consequence of molecules'
absorbing light is the creation of
transient excited states whose
chemical and physical properties differ
greatly from the original molecules.
Electrochemical reaction, any process
either caused or accompanied by the
passage of an electric current and
involving in most cases the transfer of
electrons between two substances—
one a solid and the other a liquid.