Extra 30 short-answer questions from the Chapter:1 Chemical Reactions and Equations for Class 10 CBSE Science:
1-10: Basics of Chemical Reactions
What is a chemical reaction?
A chemical reaction is a process in which one or more substances (reactants) are converted into new substances (products) with different properties.
What are reactants and products in a chemical reaction?
Reactants are the substances that undergo a chemical change, while products are the new substances formed as a result of the reaction.
State the Law of Conservation of Mass with an example.
The law states that mass can neither be created nor destroyed in a chemical reaction.
Example:
H₂ + Cl₂ → 2HCl
(Total mass of reactants = Total mass of products).
Why should a chemical equation be balanced?
A chemical equation should be balanced to satisfy the Law of Conservation of Mass, which states that the number of atoms of each element must be the same on both sides of the equation.
What is a balanced chemical equation? Give an example.
A balanced chemical equation has an equal number of atoms of each element on both reactant and product sides.
Example:
2H₂ + O₂ → 2H₂O
.
What is the difference between a physical change and a chemical change?
Physical change
: No new substance is formed (e.g., melting of ice).
Chemical change
: A new substance is formed with different properties (e.g., rusting of iron).
What are the characteristics of a chemical reaction?
Change in
colour
, evolution of gas, formation of precipitate, change in temperature, and change in state.
What happens when magnesium ribbon burns in air? Write the chemical equation.
Magnesium burns in air to form
magnesium oxide
, producing a bright white light.
2Mg + O₂ → 2MgO
.
What is an exothermic reaction? Give an example.
A reaction that releases heat energy.
Example:
CH₄ + 2O₂ → CO₂ + 2H₂O + Heat
(Combustion of methane).
What is an endothermic reaction? Give an example.
A reaction that absorbs heat energy.
Example:
CaCO
₃ →
CaO
+ CO₂
(Decomposition of calcium carbonate).
11-20: Types of Chemical Reactions
What is a combination reaction? Give an example.
A reaction where two or more substances combine to form a single product.
Example:
CaO
+ H₂O →
Ca(
OH)₂
.
What is a decomposition reaction? Give an example.
A reaction where a single compound breaks down into simpler substances.
Example:
2H₂O₂ → 2H₂O + O₂
.
What are the types of decomposition reactions?
Thermal decomposition
(Heat-based)
Electrolytic decomposition
(Electricity-based)
Photochemical decomposition
(Light-based).
What is a displacement reaction? Give an example.
A reaction in which a more reactive element displaces a less reactive element from its compound.
Example:
Zn +
CuSO
₄ →
ZnSO
₄ + Cu
.
What is a double displacement reaction? Give an example.
A reaction in which ions of two compounds are exchanged to form new compounds.
Example:
Na₂SO
₄ +
BaCl
₂ →
BaSO
₄ + 2NaCl
.
What happens when iron nails are placed in copper
sulfate
solution?
Iron displaces copper from copper
sulfate
, turning the solution from blue to green.
Fe +
CuSO
₄ →
FeSO
₄ + Cu
.
Why does the
colour
of copper
sulphate
solution change when an iron nail is dipped in it?
Iron is more reactive than copper, so it displaces copper, forming iron
sulphate
(green in
colour
).
What happens when silver chloride is exposed to sunlight?
It undergoes a photochemical decomposition reaction and turns black.
2AgCl → 2Ag + Cl₂ (Sunlight)
.
What is a redox reaction?
A reaction in which oxidation and reduction occur simultaneously.
What is oxidation and reduction?
Oxidation
: Gain of oxygen or loss of electrons.
Reduction
: Loss of oxygen or gain of electrons.
Write the balanced equation for rusting of iron.
4Fe + 3O₂ + 6H₂O → 4
Fe(
OH)₃
.
What is corrosion? Give an example.
Corrosion is the slow deterioration of metals due to environmental reactions.
Example:
Rusting of iron
.
How can rusting of iron be prevented?
By
painting, galvanization, oiling, or using stainless steel
.
What is rancidity? How can it be prevented?
Rancidity is the spoilage of food due to oxidation of fats and oils.
It can be prevented by
refrigeration, adding antioxidants, and storing in airtight containers
.
Why does food packed in chips contain nitrogen gas?
To prevent oxidation and rancidity.
What is the importance of a catalyst in a chemical reaction?
A catalyst speeds up a reaction without undergoing permanent change.
What happens when quicklime (
CaO
) reacts with water?
It forms slaked lime with the release of heat.
CaO
+ H₂O →
Ca(
OH)₂ + Heat
.
What type of reaction is used in black and white photography?
Photochemical decomposition reaction
.
Write the equation for the reaction between baking soda and vinegar.
NaHCO
₃ + CH₃COOH → CO₂ + H₂O +
CH₃COONa
.
What happens when an aqueous solution of sodium
sulphate
is mixed with barium chloride?
A white precipitate of
barium
sulphate
(
BaSO
₄)
is formed.
Na₂SO
₄ +
BaCl
₂ →
BaSO
₄ + 2NaCl
.
