Class 9 Chemistry MCQs: Chemical Equilibrium

MCQs (sample)

Showing 25 questions from this chapter. For a full timed test, use “Start online test”.

1. 1. What is equilibrium achieved when?

   • Pure reactants, pure products, or a mixture of them are placed in a closed container
   • Only products are placed in an open container
   • Reactants are continuously added to the container
   • The temperature of the system is changed
   Answer & explanation

   Correct: Pure reactants, pure products, or a mixture of them are placed in a closed container

   Equilibrium occurs when pure reactants, pure products, or a mixture is in a closed container.

2. 2. What happens to copper (II) sulphate when heated?

   • Forms anhydrous copper (II) sulphate
   • Forms hydrated copper (II) sulphate
   • Turn into gas
   • No change occurs
   Answer & explanation

   Correct: Forms anhydrous copper (II) sulphate

   Heating copper (II) sulphate removes water, forming anhydrous copper (II) sulphate, a white solid.

3. 3. What is a complete reaction?

   • A reaction with all reactants converted to products
   • A reaction that never occurs
   • A reaction that only involves solids
   • A reaction with excess reactants
   Answer & explanation

   Correct: A reaction with all reactants converted to products

   A complete reaction is defined as one in which all reactants have been converted to products.

4. 4. Which condition is NOT required for equilibrium?

   • The concentration of reactant or product remains unchanged
   • The temperature of the system remains constant
   • The pressure or volume of the system remains constant
   • The color of the reactants must change
   Answer & explanation

   Correct: The color of the reactants must change

   The change in color of reactants is not a requirement for equilibrium.

5. 5. What is the color of anhydrous copper (II) sulphate?

   • White
   • Blue
   • Pink
   • Green
   Answer & explanation

   Correct: White

   Anhydrous copper (II) sulphate is described as a white solid.

6. 6. What type of reactions are characterized by the simultaneous conversion of reactants to products and products to reactants?

   • Irreversible reactions
   • Reversible reactions
   • Endothermic reactions
   • Exothermic reactions
   Answer & explanation

   Correct: Reversible reactions

   Reversible reactions are those where reactants convert to products and products convert back to reactants simultaneously.

7. 7. What happens to the concentrations of reactants and products at equilibrium?

   • They change continuously
   • They remain the same indefinitely
   • Only reactant concentrations increase
   • Only product concentrations decrease
   Answer & explanation

   Correct: They remain the same indefinitely

   At equilibrium, the concentrations of reactants and products remain the same indefinitely.

8. 8. What is the formula of hydrated cobalt(II) chloride?

   • CoCl2
   • CoCl2.6H2O
   • CuSO4.5H2O
   • CuSO4
   Answer & explanation

   Correct: CoCl2.6H2O

   The formula for hydrated cobalt(II) chloride is CoCl2.6H2O.

9. 9. Which of the following statements is true about equilibrium reactions?

   • They end quickly.
   • Forward and reverse reactions occur simultaneously.
   • They only produce one product.
   • They do not involve collisions.
   Answer & explanation

   Correct: Forward and reverse reactions occur simultaneously.

   Equilibrium reactions involve simultaneous forward and reverse reactions at the same rate.

10. 10. How does the forward and backward movement behave at equilibrium?

    • They occur at different speeds
    • They stop completely
    • They occur at the same speed
    • Only the forward movement occurs
    Answer & explanation

    Correct: They occur at the same speed

    At equilibrium, forward and backward movements occur at the same speed.

11. 11. What happens to cobalt(II) chloride when heated?

    • It becomes pink
    • It becomes blue
    • It remains the same
    • It evaporates completely
    Answer & explanation

    Correct: It becomes blue

    When heated, cobalt(II) chloride loses water and becomes anhydrous cobalt(II) chloride, which is blue.

12. 12. In a closed container, what happens when liquid is placed inside?

    • It evaporates completely without condensing.
    • It creates an equal amount of vapor and liquid.
    • All the vapor condenses back to liquid immediately.
    • The container breaks due to pressure.
    Answer & explanation

    Correct: It creates an equal amount of vapor and liquid.

    In a closed container, the liquid evaporates and some vapor condenses until a balance is achieved between evaporation and condensation.

13. 13. Which physical condition ensures the concentration of reactants and products remains unchanged?

    • Temperature must vary
    • Pressure or volume must change
    • Concentration must remain unchanged
    • Reactants must be in excess
    Answer & explanation

    Correct: Concentration must remain unchanged

    The concentration of reactant or product must remain unchanged to maintain equilibrium.

14. 14. When water is added to anhydrous cobalt(II) chloride, what occurs?

    • It becomes blue solid
    • It becomes pink solid
    • It starts bubbling
    • It forms a gas
    Answer & explanation

    Correct: It becomes pink solid

    Adding water to anhydrous cobalt(II) chloride converts it back to hydrated cobalt(II) chloride, which is a pink solid.

15. 15. What does a double arrow in a chemical equation indicate?

    • That the reaction is complete
    • That the reaction is irreversible
    • That the reaction is reversible
    • That the reaction does not involve gases
    Answer & explanation

    Correct: That the reaction is reversible

    A double arrow indicates that a reaction is reversible, proceeding in both the forward and reverse directions.

16. 16. What happens to the system’s volume at equilibrium?

    • It must be increased
    • It must be decreased
    • It must remain constant
    • It can fluctuate wildly
    Answer & explanation

    Correct: It must remain constant

    The volume of the system must remain constant to satisfy conditions for equilibrium.

17. 17. In the equation CuSO4.5H2O <=> CuSO4 + 5H2O, what does the left side represent?

    • Anhydrous copper (II) sulphate
    • Hydrated copper (II) sulphate
    • Water only
    • Cobalt(II) chloride
    Answer & explanation

    Correct: Hydrated copper (II) sulphate

    The left side represents hydrated copper (II) sulphate, which is CuSO4.5H2O.

18. 18. What happens to the rate of the reverse reaction as the concentration of SO3 increases?

    • It decreases immediately.
    • It remains constant.
    • It accelerates.
    • It stops completely.
    Answer & explanation

    Correct: It accelerates.

    As the concentration of SO3 increases, the reverse reaction accelerates until equilibrium is reached.

19. 19. If the temperature of a system changes, what happens to its equilibrium?

    • Equilibrium is achieved immediately
    • Equilibrium conditions can be disrupted
    • Equilibrium becomes permanent
    • Equilibrium is unaffected
    Answer & explanation

    Correct: Equilibrium conditions can be disrupted

    Changing the temperature can disrupt the conditions required for equilibrium.

20. 20. What color change occurs when hydrated cobalt(II) chloride loses water?

    • From blue to pink
    • From pink to blue
    • From green to white
    • No color change
    Answer & explanation

    Correct: From pink to blue

    Hydrated cobalt(II) chloride changes color from pink to blue when it loses water and becomes anhydrous.

21. 21. What is the state called when forward and reverse reactions occur at the same rate?

    • Chemical change
    • Dynamic equilibrium
    • Physical change
    • Chemical completion
    Answer & explanation

    Correct: Dynamic equilibrium

    The state of a chemical reaction where forward and reverse reactions occur at the same rate is called dynamic equilibrium.

22. 22. Which statement about the conditions for equilibrium is true?

    • Only the products concentration can change
    • Either pressure, volume, or concentrations must change
    • All physical conditions must remain constant
    • Temperature must fluctuate periodically
    Answer & explanation

    Correct: All physical conditions must remain constant

    All physical conditions must remain constant to maintain equilibrium.

23. 23. What is the effect of adding water to anhydrous copper (II) sulphate?

    • It forms white solid
    • It forms blue solid
    • It remains unchanged
    • It evaporates
    Answer & explanation

    Correct: It forms blue solid

    Adding water to anhydrous copper (II) sulphate forms hydrated copper (II) sulphate, which is a blue solid.

24. 24. What does chemical equilibrium imply about the concentrations of reactants and products?

    • They continuously change.
    • They become constant.
    • They only favor reactants.
    • They only favor products.
    Answer & explanation

    Correct: They become constant.

    At equilibrium, the concentration of reactants and products remains constant despite continuous reaction at the molecular level.

25. 25. What type of container is necessary for achieving equilibrium?

    • Open container
    • Closed container
    • Plastic container
    • Glass container
    Answer & explanation

    Correct: Closed container

    Equilibrium is achieved in a closed container.