Class 10 Science Lesson 15

Exercise

1. Choose the correct option for the following questions.

a) What type of chemical reaction is the reaction between sodium chloride and silver nitrate?

i. Combination reaction
ii. Single displacement reaction
iii. Decomposition reaction
iv. Double displacement reaction

Answer: iv. Double displacement reaction

b) What type of reaction is 4Na + O₂ → 2Na₂O?

i. Addition reaction
ii. Decomposition reaction
iii. Acid base reaction
iv. Displacement reaction

Answer: i. Addition reaction

c) Which substance is X in the given chemical reaction?
HCl + X → NaCl + H₂O

i. NaOH
ii. Na
iii. NaH
iv. Na + H₂O

Answer: i. NaOH

d) What type of reaction is the heating of CaCO₃?

i. Combination reaction
ii. Single displacement reaction
iii. Decomposition reaction
iv. Double displacement reaction

Answer: iii. Decomposition reaction

2. Give Reason:

i) Hydrogen peroxide is not stored in a transparent vessel:

Ans: Hydrogen peroxide (H₂O₂) is unstable and decomposes slowly when exposed to light. To prevent this, it is stored in dark or opaque (usually brown) bottles to block light, which slows down its decomposition.

ii) Acid-base reaction is also known as neutralization reaction:

Ans: An acid-base reaction is called a neutralization reaction because the hydrogen ions (H⁺) from the acid react with the hydroxide ions (OH⁻) from the base to form water (H₂O), a neutral substance. This process also results in the formation of a salt, and the acidic and basic properties are neutralized.

iii. The rate of chemical reaction is different according to the type of the reaction:

Ans: Different types of chemical reactions proceed at different speeds depending on the nature of the reactants and the reaction mechanism. For example, reactions involving ions in solution (like double displacement) are usually faster, while reactions involving breaking strong bonds (like decomposition) are slower. Reaction rate is also affected by factors like temperature, pressure, and catalysts, depending on the type of reaction.

3. Write Differences Between:

a) Single and double displacement reaction

b. Combination and decomposition reaction

4. Balance the following chemical reactions and mention their types:

a) KClO → 2KCl + 3O₂

Balanced: 2KClO₃ → 2KCl + 3O₂
Type: Decomposition reaction

b) CH₄ + O₂ → CO₂ + H₂O

Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O
Type: Combustion reaction (also an oxidation reaction)

c) Fe + O₂ → Fe₂O₃

Balanced: 4Fe + 3O₂ → 2Fe₂O₃
Type: Combination reaction

d) Zn + H₂SO₄ → ZnSO₄ + H₂

Balanced: Zn + H₂SO₄ → ZnSO₄ + H₂
Type: Single displacement reaction

e) Al + H₂SO₄ → Al₂(SO₄)₃ + H₂

Balanced: 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂
Type: Single displacement reaction

5. Answer the following questions:

a) What do you mean by a chemical reaction? Explain with an example.

Answer: A chemical reaction is a process in which one or more substances (reactants) are transformed into new substances (products) with different physical and chemical properties. During this process, chemical bonds are broken and new bonds are formed.

Example:
CH₄ + 2O₂ → CO₂ + 2H₂O

In this combustion reaction, methane (CH₄) reacts with oxygen (O₂) to form carbon dioxide (CO₂) and water (H₂O).

b) What is the rate of chemical reaction? Write any four factors which affect the rate of chemical reaction.

Answer: The rate of chemical reaction refers to how fast or slow a chemical reaction takes place — i.e., the speed at which reactants are converted into products.

Four factors affecting the rate of chemical reaction:

1. Temperature – Increasing temperature generally increases the reaction rate.
2. Concentration of reactants – Higher concentration leads to a faster reaction.
3. Surface area of reactants – More surface area increases the reaction rate.
4. Presence of a catalyst – Catalysts speed up the reaction without being consumed.

c) What do you mean by a displacement reaction? Write its two examples with their balanced chemical equations.

Answer: A displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound.

Examples:

1. Zn + CuSO₄ → ZnSO₄ + Cu
   Zinc displaces copper from copper sulfate.
2. Fe + CuSO₄ → FeSO₄ + Cu
   Iron displaces copper from copper sulfate.

d) Write two examples of decomposition reactions with balanced chemical equations.

Answer: A decomposition reaction is a type of chemical reaction in which a single compound breaks down into two or more simpler substances.

Examples:

1. 2H₂O₂ → 2H₂O + O₂
   (Hydrogen peroxide decomposes into water and oxygen)

CaCO₃ → CaO + CO₂
(Calcium carbonate decomposes into calcium oxide and carbon dioxide)

e) What is the type of chemical reaction occurring inside the test tube shown in the given figure? Write the balanced chemical equation of that reaction. (Reaction of cupper sulphate with iron)

Answer:

Solution:

Type of reaction: Displacement Reaction
Balanced Reaction: Fe + CuSO₄ → FeSO₄ + Cu

f) Four students A, B, C, and D are allowed to carry out decomposition reactions in the laboratory. All of them perform it differently as given below.

i. Student A burnt magnesium (Mg) ribbon
ii. Student B mixed Zn in FeSO₄ solution
iii. Student C heated KClO₃ in a hard glass test tube
iv. Student D mixed Zn and HCl solution

Which student followed the correct procedure? Write the balanced chemical reaction of that process.

Answer:

Student C followed the correct procedure. Heating potassium chlorate (KClO₃) is a decomposition reaction, as it breaks down into simpler substances upon heating.

Balanced chemical reaction:

2KClO3→2KCl+3O2↑

g) Samir burns a magnesium ribbon which is like a small strip or a ribbon. It burns brightly and forms white ash ‘A’.

Write the name of substance ‘A’. Write a balanced chemical reaction of the process.

Answer:

The substance ‘A’ is magnesium oxide (MgO).

Balanced chemical reaction:
2Mg+O2→2MgO