Chemical Reactions and Equations (Class 10, CBSE)(mock test -30)

 

Practice Questions – Chemical Reactions and Equations (Class 10, CBSE)(mock test -30)

A. Multiple Choice Questions (MCQs)

  1. Which of the following is an endothermic reaction?
    a) Burning of coal
    b) Respiration
    c) Photosynthesis
    d) Condensation of steam

  2. Which law is followed while balancing chemical equations?
    a) Law of definite proportion
    b) Law of multiple proportion
    c) Law of conservation of mass
    d) Law of constant composition

  3. Which of the following is a double displacement reaction?
    a) Zn + H2SO4 → ZnSO4 + H2
    b) 2H2O → 2H2 + O2
    c) Na2SO4 + BaCl2 → BaSO4 + 2NaCl
    d) CH4 + 2O2 → CO2 + 2H2O

  4. Which of the following shows a chemical change?
    a) Melting of ice
    b) Burning of candle
    c) Dissolving sugar in water
    d) Breaking glass

  5. In the reaction:
    2Mg + O2 → 2MgO
    Which substance is oxidized?

B. Assertion-Reason Questions

For each question, choose:
(a) Both A and R are true, R is the correct explanation
(b) Both A and R are true, but R is not the correct explanation
(c) A is true, R is false
(d) A is false, R is true

  1. Assertion (A): Respiration is considered an exothermic reaction.
    Reason (R): Energy is released when glucose is broken down in the presence of oxygen.

  2. Assertion (A): When ferrous sulphate crystals are heated, a brown solid is formed.
    Reason (R): Heating causes decomposition of ferrous sulphate into ferric oxide, SO2, and SO3.

  3. Assertion (A): In the reaction CuO + H2 → Cu + H2O, copper oxide is reduced.
    Reason (R): Loss of oxygen is termed as reduction.

C. Short Answer Questions

  1. Define a balanced chemical equation. Why is it necessary to balance an equation?

  2. Write balanced chemical equations for the following:
    (i) Decomposition of calcium carbonate.
    (ii) Reaction of sodium hydroxide with hydrochloric acid.
    (iii) Photosynthesis reaction.

  3. A solution of substance X is used for whitewashing walls. Name the substance X and write the chemical equations of the reactions involved.

  4. Write observations and equations for the following:
    (i) Heating of lead nitrate crystals.
    (ii) Adding dilute HCl to sodium carbonate solution.

  5. Give one example each of:
    (i) Combination reaction
    (ii) Displacement reaction
    (iii) Double displacement reaction
    (iv) Redox reaction

D. Long Answer Questions

  1. What is a chemical reaction? State any four characteristics of chemical reactions with suitable examples.

  2. Differentiate between physical and chemical changes with two examples each.

  3. Explain the following with balanced chemical equations:
    (i) Electrolysis of water
    (ii) Rusting of iron
    (iii) Neutralization reaction

  4. What happens when silver chloride is exposed to sunlight? Write the balanced chemical equation and mention one application of this reaction.

  5. A student burns magnesium ribbon in air. Answer the following:
    (i) Why should the ribbon be cleaned before burning?
    (ii) What type of reaction takes place?
    (iii) Write the balanced chemical equation.

  6. Classify the following into combination, decomposition, displacement, double displacement, or redox reactions:
    (i) Fe + CuSO4 → FeSO4 + Cu
    (ii) CaCO3 → CaO + CO2
    (iii) N2 + 3H2 → 2NH3
    (iv) Zn + 2HCl → ZnCl2 + H2
    (v) 2AgCl → 2Ag + Cl2


Answers – Practice Questions

A. Multiple Choice Questions (MCQs)

1. c) Photosynthesis → It absorbs energy (endothermic).
2. c) Law of conservation of mass
3. c) Na2SO4 + BaCl2 → BaSO4 + 2NaCl (double displacement)
4. b) Burning of candle (chemical change)
5. Mg is oxidized (since it gains oxygen).

B. Assertion-Reason Questions

6. (a) Both A and R are true, and R explains A.
7. (a) Both A and R are true, and R explains A.
8. (a) Both A and R are true, and R explains A.

C. Short Answer Questions

9.

  • Balanced chemical equation: The number of atoms of each element on both sides of the equation is equal.
  • Necessary because it obeys the law of conservation of mass (mass can neither be created nor destroyed).

10.
(i) CaCO3 → CaO + CO2
(ii) NaOH + HCl → NaCl + H2O
(iii) 6CO2 + 6H2O → C6H12O6 + 6O2

11.

  • Substance X = Calcium hydroxide [Ca(OH)2].
  • CaO + H2O → Ca(OH)2
  • Ca(OH)2 + CO2 → CaCO3 + H2O

12.
(i) Heating lead nitrate → Brown gas (NO2) and oxygen released.
2Pb(NO3)2 → 2PbO + 4NO2 + O2
(ii) Adding HCl to Na2CO3 → Effervescence due to CO2 gas.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2

13.
(i) Combination → 2H2 + O2 → 2H2O
(ii) Displacement → Zn + CuSO4 → ZnSO4 + Cu
(iii) Double displacement → AgNO3 + NaCl → AgCl + NaNO3
(iv) Redox → CuO + H2 → Cu + H2O

D. Long Answer Questions

14.

  • A chemical reaction is a process where one or more substances (reactants) are transformed into new substances (products).
  • Characteristics:
    1. Change in state (e.g., H2 + O2 → H2O)
    2. Change in colour (e.g., Fe + CuSO4 → FeSO4 + Cu)
    3. Evolution of gas (e.g., Zn + HCl → ZnCl2 + H2)
    4. Change in temperature (CaO + H2O → Ca(OH)2 + Heat)

15.

  • Physical changes: No new substance formed (melting ice, dissolving sugar).
  • Chemical changes: New substance formed (rusting of iron, burning of paper).

16.
(i) Electrolysis of water: 2H2O → 2H2 + O2
(ii) Rusting: Fe + O2 + H2O → Fe2O3·xH2O
(iii) Neutralization: NaOH + HCl → NaCl + H2O

17.

  • Silver chloride decomposes in sunlight:
    2AgCl → 2Ag + Cl2
  • Application: Black-and-white photography.

18.
(i) Magnesium ribbon is cleaned to remove oxide coating.
(ii) Combination reaction.
(iii) 2Mg + O2 → 2MgO

19.
(i) Displacement
(ii) Decomposition
(iii) Combination
(iv) Displacement
(v) Decomposition (Photochemical)


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