Unit 15: Chemical Reactions - Exercise Solutions

Unit 15: Chemical Reactions

Complete Exercise Solutions — Class 10 Science & Technology

A. Multiple Choice Questions
1. What type of chemical reaction is this?
NaCl + AgNO₃ → AgCl + NaNO₃
i. Combination
ii. Decomposition
iii. Single displacement
iv. Double displacement
2. The reaction: 2KClO₃ → 2KCl + 3O₂ is an example of which of the following chemical reaction?
i. Combination
ii. Decomposition
iii. Displacement
iv. Double displacement
3. Which of the following is a neutralization reaction?
i. C + O₂ → CO₂
ii. CaCO₃ → CaO + CO₂
iii. Zn + H₂SO₄ → ZnSO₄ + H₂
iv. HCl + NaOH → NaCl + H₂O
4. In the reaction: Zn + 2HCl → ZnCl₂ + H₂, which species is getting displaced (i.e., the displaced element)?
i. Zn
ii. H
iii. Cl
iv. HCl
5. What is the balanced form of the following chemical equation?
C₂H₆ + O₂ → CO₂ + H₂O
i. C₂H₆ + 4O₂ → 2CO₂ + 3H₂O
ii. C₂H₆ + 3O₂ → 2CO₂ + 3H₂O
iii. 2C₂H₆ + 5O₂ → 4CO₂ + 6H₂O
iv. 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O
6. The decomposition of hydrogen peroxide is often catalyzed by a substance. Which of these is used as a catalyst/promoter for that reaction?
i. Silver
ii. Manganese dioxide (MnO₂)
iii. Platinum
iv. Sodium chloride
7. Which factor does NOT affect the rate of a chemical reaction?
i. Temperature
ii. Concentration of reactants
iii. Shape of the container (if volume remains same)
iv. Presence of a catalyst
8. Which reaction describes a single displacement?
i. Fe + CuSO₄ → FeSO₄ + Cu
ii. HCl + NaOH → NaCl + H₂O
iii. N₂ + 3H₂ → 2NH₃
iv. 2KClO₃ → 2KCl + 3O₂
9. A reaction in which two reacting compounds exchange ions to form two new compounds is called:
i. Combination
ii. Decomposition
iii. Single displacement
iv. Double displacement
10. The reaction: CaCO₃ Δ→ CaO + CO₂ occurs when heated. What type of reaction is this?
i. Combination
ii. Decomposition
iii. Displacement
iv. Double displacement
11. In the given options, the combination of test tube D reacts faster out of all four. What could be the reason? (Test tube D contains Powder Zn + Dil. HCl)
i. Temperature
ii. Surface area
iii. Catalyst
iv. Light
B. Very Short Answer Type Questions
12. What is a chemical equation?
A chemical equation is the symbolic representation of a chemical reaction using the symbols and formulae of the reactants and products involved.
13. A compound is heated and forms two smaller products. What type of reaction is this?
It is a Decomposition reaction (specifically, a thermal decomposition reaction).
14. Write the general word equation for the reaction between an acid and a metal.
Metal + Dilute Acid → Salt + Hydrogen Gas
15. Name the gas released when zinc reacts with dilute hydrochloric acid.
Hydrogen gas (H₂).
16. What happens to magnesium ribbon when it is burnt in air?
It burns with a dazzling white flame to form a white powder called Magnesium oxide (MgO).
17. Write the chemical equation for the reaction between calcium oxide and water.
CaO + H₂O → Ca(OH)₂ + Heat (Calcium hydroxide is formed).
18. Which type of reaction is represented by: 2HgO Δ→ 2Hg + O₂?
Thermal Decomposition Reaction.
19. Write an example of a displacement reaction.
Fe + CuSO₄ → FeSO₄ + Cu
20. What is formed when sodium reacts with water?
Sodium hydroxide (NaOH) and Hydrogen gas (H₂) are formed.
21. Identify the reactants and products in the reaction: C + O₂ Δ→ CO₂
Reactants: Carbon (C) and Oxygen (O₂)
Product: Carbon dioxide (CO₂)
C. Short Answer Type Questions
22. Write any two differences between combination and decomposition reaction.
1. Combination Reaction: Two or more reactants combine to form a single product (e.g., 2H₂ + O₂ → 2H₂O).
2. Decomposition Reaction: A single reactant breaks down into two or more simpler products (e.g., 2H₂O → 2H₂ + O₂).
23. Why are decomposition reactions called opposite of combination reactions? Explain.
Decomposition reactions are the opposite of combination reactions because in a combination reaction, multiple simple substances combine to form a single complex compound, whereas in a decomposition reaction, a single complex compound breaks down into two or more simpler substances. For example:
• Combination: A + B → AB
• Decomposition: AB → A + B
24. Give an example of displacement reaction and acid base reaction.
• Displacement Reaction: Zn + H₂SO₄ → ZnSO₄ + H₂
• Acid-Base Reaction: HCl + NaOH → NaCl + H₂O
25. What are the factors that affect a chemical reaction?
The main factors that affect the rate of a chemical reaction are:
  1. Heat / Temperature
  2. Surface area of solid reactants
  3. Concentration of reactants
  4. Presence of a Catalyst
  5. Light and Pressure
26. Write the balanced chemical equation of the experiment given in the figure (Standard Class 10 Laboratory Preparation of Hydrogen Gas).
Zn + 2HCl → ZnCl₂ + H₂ ↑
D. Long Answer Type Questions
27. What are the main four types of reactions? Give an example of each of them.
1. Combination Reaction: Two or more reactants form one product.
2Mg + O₂ → 2MgO

2. Decomposition Reaction: One reactant breaks down into multiple products.
2KClO₃ → 2KCl + 3O₂

3. Displacement Reaction: An atom/ion in a molecule is replaced by another.
Fe + CuSO₄ → FeSO₄ + Cu

4. Double Displacement (Neutralization) Reaction: Reactants exchange ions to form new compounds.
HCl + NaOH → NaCl + H₂O
28. Identify the types of chemical reaction from the followings, and justify the type and balance the equations.
Code Balanced Chemical Equation Type of Reaction Justification
W 2Mg + O₂ → 2MgO Combination Two separate elements combine together to produce a single chemical compound.
X NaOH + HCl → NaCl + H₂O Neutralization / Double Displacement An acid and a base exchange ions to form neutral salt and water.
Y 2CaO Δ→ 2Ca + O₂ Decomposition A single compound breaks down into its constituent elements by heating.
Z Zn + 2HCl → ZnCl₂ + H₂ Single Displacement A more reactive metal (Zn) displaces a less reactive element (H) from its acid solution.
29. Give an example of a chemical equation in which the reaction factor is light, heat, electricity, or catalyst.
• Light: 2AgCl ⎯⎯Light⎯→ 2Ag + Cl₂
• Heat: CaCO₃ ⎯⎯Δ⎯→ CaO + CO₂
• Electricity: 2H₂O ⎯⎯Electricity⎯→ 2H₂ + O₂
• Catalyst: 2H₂O₂ ⎯⎯MnO₂⎯→ 2H₂O + O₂
30. Study the following data and answer: Zinc of which test tube would react fastest with an equal amount of dil. Hydrochloric acid? Which reaction factor plays the role, and what is its relationship with the rate?
• Answer: Zinc in Test Tube C (which has the largest total surface area of 22 cm²) will react the fastest.
• Reaction Factor: Total surface area of solid reactants.
• Relationship: The rate of a chemical reaction is directly proportional to the surface area of solid reactants. Increasing the surface area increases active collisions, accelerating the reaction.