Chemical reactions involve chemical changes and the formation of new products. There are four main signs that a chemical reaction has occurred: a change in color, evolution of a gas, change in temperature, or change in state. There are five main types of chemical reactions: combination, decomposition, single displacement, double displacement, and redox. Combination reactions involve reactants combining to form products. Decomposition reactions involve a single reactant breaking down into simpler products. Displacement reactions involve a more reactive element displacing a less reactive one. Redox reactions involve the gain or loss of oxygen.

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. Signs of Chemical Reactions
There are four main signs that indicate a chemical reaction has taken place:
change in color Evolution of a gas Change in temperature Change in state

4. 1. COMBINATION REACTION
(SYNTHESIS)
2. DECOMPOSITION REACTION
3. SINGLE DISPLACEMENT REACTION
4. DOUBLE DISPLACEMENT REACTION
5. REDOX REACTION

5.  These type of reactions occur when two
reactants combine to form one or more
products.
 A + B  AB
 E.g
C + O2 CO2
 They are generally exothermic reactions
which involve evolution of heat during
reaction.

6. Combination Reaction
General form: A + B  AB
element or element or compound
compound compound
Na
ClNa
Cl
2 Na + Cl2  2 NaCl

ClNa
Na
Cl

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

8. H
H
H
H
Decomposition Reaction
H
H
H
H
O
Decomposition reaction
2 H2O 2 H2 O2
General form: AB A B
+
+
+
compound two or more elements
or compounds
OO
O

9. • 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
A + BC  AC + B
AB + CD  AD + CB

10. SINGLE AND DOUBLE
DISPLACEMENT REACTIONS
Double-replacement reaction
CaCO3 + 2 HCl  CaCl2 + H2CO3
General form:
AB + CD  AD + CB
Single-replacement reaction
Mg + CuSO4  MgSO4 + Cu
General form:
A + BC  AC + B

11. PbI2
K1+
Pb2+
lead (II) chloride + potassium iodide
Cl2 I
Pb2+
Pb
K1+
K
Cl1- I1-
Cl1-
I1-
KCl
potassium chloride lead (II) iodide+
(aq) (ppt)
+ +

12. Double Displacement Reaction
K2CO3 (aq)
Potassium carbonate
BaCl2 (aq)
Barium chloride
2 KCl (aq)
Potassium chloride
BaCO3 (s)
Barium carbonate
+ +

13. Ca
Foiled again –
Aluminum loses to Calcium
Element Reactivity

14. • 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. E.g. –
OXIDATION
CuO + H2 Cu +H2O