CHAPTER 1: CHEMICAL REACTIONS AND EQUATIONS
1.Define
a)Chemical reaction- It is a chemical change in which new substances are formed,
b)Reactants - The substances that undergo a chemical reaction are called reactants.
c)Products - The new substances formed in a chemical reaction are called products
eg: 2Mg + O2 → 2MgO ,
In this reaction Mg and O2 are reactants and MgO is the product.
2.List the observations which help us to determine whether a chemical reaction has taken
place.
Ans:1. Change in state eg: 2H2(g) + O2(g) → 2H2O(l)
2Change in colour eg: Fe + Cu SO4 → FeSO4 + Cu
(blue) (pale green)
3.Change in temperature eg: CaO + H2O → Ca (OH)2 + Heat
4.Evolution of gas . eg: Zn + 2HCl → ZnCl2 + H2
5.Formation of precipitate. eg: Pb(NO3)2 + 2KI → PbI2 + 2KNO3
6.Change in smell. eg : Decaying of food
3 What do you observe in the following chemical reactions?
a) When Magnesium ribbon is heated
Ans:1.It burns with a dazzling white flame.
2.White ash is produced.
2Mg + O2 → 2MgO
b) When Lead nitrate solution is mixed with Potassium iodide solution
Ans:1. A precipitate of Lead iodide is formed.
2. It is yellowish in colour.
Pb(NO3)2 + 2KI → PbI2 + 2KNO3
(Yellow ppt)
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, c) When Zinc granules are added to dilute Sulphuric acid.
Ans: 1.Evolution of H2 gas
2.Heat is produced.
Zn + H2SO4 → ZnSO4 + H2 + Heat
4.Define:
a) Chemical equation - It represents a chemical reaction by using symbols and chemical
formulae.
b) Skeletal chemical equation - It is an unbalanced chemical equation.
c) Balanced chemical equation - The chemical equation in which the number of atoms of each
element is same on the reactant side and product side is called balanced chemical equation.
5.Why should chemical equations be balanced?
Ans: According to the law of conservation of mass ,”Mass can neither be created nor be
destroyed in a chemical reaction” .So the number of atoms of each element should be the
same on the reactant and product side.
6.How can you write a balanced chemical equation more informative?
Ans:1.By writing the physical states of the reactants and products.
Eg: Solid state by (s)
Liquid state by (l)
Gaseous state by (g)
Aqueous state by (aq)
2Mg (S) + O2(g) → 2MgO(S)
2.By writing the reaction conditions such as temperature ,pressure ,catalyst etc above or
below the arrow in the equation.
340𝑎𝑡𝑚
Eg: CO (g) + 2H2(g) > CH3OH(l)
7.BALANCE THE FOLLOWING CHEMICAL EQUATIONS:
Done in the class.
______________________________________________________________________________
TYPES OF CHEMICAL REACTIONS
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1.Define
a)Chemical reaction- It is a chemical change in which new substances are formed,
b)Reactants - The substances that undergo a chemical reaction are called reactants.
c)Products - The new substances formed in a chemical reaction are called products
eg: 2Mg + O2 → 2MgO ,
In this reaction Mg and O2 are reactants and MgO is the product.
2.List the observations which help us to determine whether a chemical reaction has taken
place.
Ans:1. Change in state eg: 2H2(g) + O2(g) → 2H2O(l)
2Change in colour eg: Fe + Cu SO4 → FeSO4 + Cu
(blue) (pale green)
3.Change in temperature eg: CaO + H2O → Ca (OH)2 + Heat
4.Evolution of gas . eg: Zn + 2HCl → ZnCl2 + H2
5.Formation of precipitate. eg: Pb(NO3)2 + 2KI → PbI2 + 2KNO3
6.Change in smell. eg : Decaying of food
3 What do you observe in the following chemical reactions?
a) When Magnesium ribbon is heated
Ans:1.It burns with a dazzling white flame.
2.White ash is produced.
2Mg + O2 → 2MgO
b) When Lead nitrate solution is mixed with Potassium iodide solution
Ans:1. A precipitate of Lead iodide is formed.
2. It is yellowish in colour.
Pb(NO3)2 + 2KI → PbI2 + 2KNO3
(Yellow ppt)
1|Page
, c) When Zinc granules are added to dilute Sulphuric acid.
Ans: 1.Evolution of H2 gas
2.Heat is produced.
Zn + H2SO4 → ZnSO4 + H2 + Heat
4.Define:
a) Chemical equation - It represents a chemical reaction by using symbols and chemical
formulae.
b) Skeletal chemical equation - It is an unbalanced chemical equation.
c) Balanced chemical equation - The chemical equation in which the number of atoms of each
element is same on the reactant side and product side is called balanced chemical equation.
5.Why should chemical equations be balanced?
Ans: According to the law of conservation of mass ,”Mass can neither be created nor be
destroyed in a chemical reaction” .So the number of atoms of each element should be the
same on the reactant and product side.
6.How can you write a balanced chemical equation more informative?
Ans:1.By writing the physical states of the reactants and products.
Eg: Solid state by (s)
Liquid state by (l)
Gaseous state by (g)
Aqueous state by (aq)
2Mg (S) + O2(g) → 2MgO(S)
2.By writing the reaction conditions such as temperature ,pressure ,catalyst etc above or
below the arrow in the equation.
340𝑎𝑡𝑚
Eg: CO (g) + 2H2(g) > CH3OH(l)
7.BALANCE THE FOLLOWING CHEMICAL EQUATIONS:
Done in the class.
______________________________________________________________________________
TYPES OF CHEMICAL REACTIONS
2|Page
