SCIENCE
CLASS-10
,
, CHAPTER 1
CHEMICAL REACTIONS AND EQUATIONS
Syllabus for 2020-21 : Chemical equation, Balanced chemical equation, implications of
a balanced chemical equation, types of chemical reactions: combination,
decomposition, displacement, double displacement, precipitation, neutralization,
oxidation and reduction.
TYPES OF CHEMICAL REACTIONS : (3)
1. COMBINATION REACTION
A reaction in which two or more reactants combine to form a single product is called a combination
reaction.
E.g. C + O2 → CO2
2. DECOMPOSITION REACTION
A reaction in which a compound splits into two or more simple substances is called a decomposition
reaction.
a) Thermal decomposition : When decomposition is carried out by heating.
E.g. CaCO3 → CaO + CO2
b) Electrolytic decomposition : When decomposition is carried out by passing electricity.
E.g. 2H2O → 2H2 + O2
c) Photolytic decomposition : When decomposition is carried out in presence of sunlight.
E.g. 2AgCl → 2Ag +Cl2
White coloured silver chloride turns grey on exposure to sunlight.
This reaction is used in black and white photography.
3. DISPLACEMENT REACTION
The chemical reaction in which a more reactive element displaces a less reactive element from its salt
solution is called displacement reaction.
E.g. Fe + CuSO4 → FeSO4 + Cu
The blue colour of copper sulphate changes to pale green colour due to the formation of ferrous sulphate
and brown coloured deposition of copper is observed.
, 4. DOUBLE DISPLACEMENT REACTION
A reaction in which new compounds are formed by mutual exchange of ions between the reactants is called
double displacement reaction.
E.g. Na2SO4 + BaCl2 → BaSO4 + 2NaCl
White precipitate of barium sulphate is formed, so it is also called a precipitation reaction.
5. OXIDATION AND REDUCTION/REDOX REACTION (2)
Oxidation : Addition of oxygen to reactant / Removal of hydrogen from a reactant.
C + O2 → CO2
Reduction : Addition of hydrogen to reactant/ Removal of oxygen from reactant.
CuO + H2 → Cu + H2O
In this reaction, substance oxidized is H2 and substance reduced is CuO.
CuO is oxidizing agent and H2 is reducing agent.
Since oxidation and reduction are taking place together, it is a redox reaction.
QUESTIONS
1. Give reason why
a) Iron displaces copper from copper sulphate solution.
b) We store silver chloride in dark coloured bottles in labs. (2)
2. A small amount of Ferrous sulphate is heated in hard glass tube.
a) Write the balanced chemical reaction involved.
b) Name the type of reaction taking place. (2)
3. (a) Identify (i) the reducing and oxidizing agents (ii) substance getting oxidized and reduced in the
given chemical reaction : CuO + H2 → Cu + H2O
(b) Give an example of a double displacement reaction. (3)
CLASS-10
,
, CHAPTER 1
CHEMICAL REACTIONS AND EQUATIONS
Syllabus for 2020-21 : Chemical equation, Balanced chemical equation, implications of
a balanced chemical equation, types of chemical reactions: combination,
decomposition, displacement, double displacement, precipitation, neutralization,
oxidation and reduction.
TYPES OF CHEMICAL REACTIONS : (3)
1. COMBINATION REACTION
A reaction in which two or more reactants combine to form a single product is called a combination
reaction.
E.g. C + O2 → CO2
2. DECOMPOSITION REACTION
A reaction in which a compound splits into two or more simple substances is called a decomposition
reaction.
a) Thermal decomposition : When decomposition is carried out by heating.
E.g. CaCO3 → CaO + CO2
b) Electrolytic decomposition : When decomposition is carried out by passing electricity.
E.g. 2H2O → 2H2 + O2
c) Photolytic decomposition : When decomposition is carried out in presence of sunlight.
E.g. 2AgCl → 2Ag +Cl2
White coloured silver chloride turns grey on exposure to sunlight.
This reaction is used in black and white photography.
3. DISPLACEMENT REACTION
The chemical reaction in which a more reactive element displaces a less reactive element from its salt
solution is called displacement reaction.
E.g. Fe + CuSO4 → FeSO4 + Cu
The blue colour of copper sulphate changes to pale green colour due to the formation of ferrous sulphate
and brown coloured deposition of copper is observed.
, 4. DOUBLE DISPLACEMENT REACTION
A reaction in which new compounds are formed by mutual exchange of ions between the reactants is called
double displacement reaction.
E.g. Na2SO4 + BaCl2 → BaSO4 + 2NaCl
White precipitate of barium sulphate is formed, so it is also called a precipitation reaction.
5. OXIDATION AND REDUCTION/REDOX REACTION (2)
Oxidation : Addition of oxygen to reactant / Removal of hydrogen from a reactant.
C + O2 → CO2
Reduction : Addition of hydrogen to reactant/ Removal of oxygen from reactant.
CuO + H2 → Cu + H2O
In this reaction, substance oxidized is H2 and substance reduced is CuO.
CuO is oxidizing agent and H2 is reducing agent.
Since oxidation and reduction are taking place together, it is a redox reaction.
QUESTIONS
1. Give reason why
a) Iron displaces copper from copper sulphate solution.
b) We store silver chloride in dark coloured bottles in labs. (2)
2. A small amount of Ferrous sulphate is heated in hard glass tube.
a) Write the balanced chemical reaction involved.
b) Name the type of reaction taking place. (2)
3. (a) Identify (i) the reducing and oxidizing agents (ii) substance getting oxidized and reduced in the
given chemical reaction : CuO + H2 → Cu + H2O
(b) Give an example of a double displacement reaction. (3)
