Class 9 Chemistry MCQs: Energetics

MCQs (sample)

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

1. 1. What does activation energy refer to in a chemical reaction?

   • Minimum energy required for effective collisions
   • Energy released during a reaction
   • Total kinetic energy of particles
   • Energy needed to break all chemical bonds
   Answer & explanation

   Correct: Minimum energy required for effective collisions

   Activation energy is defined as the minimum amount of energy that particles must have for effective collisions to occur.

2. 2. What is bond dissociation energy?

   • Energy required to break one mole of a particular bond to form neutral atoms
   • Energy released when forming one mole of a bond
   • Energy absorbed when a reaction takes place
   • Energy used to form bonds in a chemical reaction
   Answer & explanation

   Correct: Energy required to break one mole of a particular bond to form neutral atoms

   Bond dissociation energy is defined as the amount of energy required to break one mole of a particular bond to form neutral atoms.

3. 3. What happens to energy during a chemical reaction?

   • Energy is developed or absorbed.
   • Energy is always released.
   • Energy cannot change.
   • Energy is created from nothing.
   Answer & explanation

   Correct: Energy is developed or absorbed.

   Energy in the form of heat is developed or absorbed as a result of a chemical reaction.

4. 4. What is the enthalpy of reaction?

   • The amount of heat evolved or absorbed in a chemical reaction.
   • The total energy of a system at constant volume.
   • The pressure of a gas in a closed container.
   • The temperature difference between reactants and products.
   Answer & explanation

   Correct: The amount of heat evolved or absorbed in a chemical reaction.

   Enthalpy of reaction is defined as the amount of heat or thermal energy evolved or absorbed in a chemical reaction.

5. 5. What is a thermochemical reaction?

   • A reaction that absorbs or evolves heat.
   • A reaction that occurs without heat change.
   • A chemical change that only involves light.
   • A reaction that produces gases only.
   Answer & explanation

   Correct: A reaction that absorbs or evolves heat.

   A thermochemical reaction is defined as one that proceeds with the evolution or absorption of heat.

6. 6. What is respiration?

   • A biochemical process that releases energy from food
   • A process that produces glucose
   • A method of oxygen absorption
   • A hormonal response to exercise
   Answer & explanation

   Correct: A biochemical process that releases energy from food

   Respiration is defined as a biochemical process in which energy is released from food.

7. 7. What is a catalyst?

   • A substance that accelerates a chemical reaction and remains unchanged.
   • A substance that is consumed during a chemical reaction.
   • A solution used to slow down chemical reactions.
   • A product formed from a chemical reaction.
   Answer & explanation

   Correct: A substance that accelerates a chemical reaction and remains unchanged.

   A catalyst is defined as a substance that accelerates a chemical reaction but remains chemically unchanged at the end.

8. 8. According to collision theory, what is essential for a chemical reaction to occur?

   • Particles must collide with high energy and proper orientation
   • Particles must be at low temperatures
   • Particles must be in a gaseous state only
   • Particles must collide infinitely many times
   Answer & explanation

   Correct: Particles must collide with high energy and proper orientation

   For a chemical reaction to occur, particles must collide with sufficient energy and in the correct orientation.

9. 9. What happens when a bond is formed?

   • Energy is absorbed
   • Energy is released
   • No energy change occurs
   • Energy is converted to heat
   Answer & explanation

   Correct: Energy is released

   Forming a bond always releases energy.

10. 10. What occurs when old bonds are broken in a chemical reaction?

    • Energy is released.
    • Energy is consumed.
    • Energy remains constant.
    • Energy is developed.
    Answer & explanation

    Correct: Energy is consumed.

    Breaking bonds always consumes energy in a chemical reaction.

11. 11. What is the sign of enthalpy change for exothermic reactions?

    • Positive
    • Negative
    • Zero
    • Varies
    Answer & explanation

    Correct: Negative

    For exothermic reactions, the sign of enthalpy change is negative, indicating that heat is evolved.

12. 12. Which type of reaction absorbs heat from the surroundings?

    • Exothermic reaction
    • Endothermic reaction
    • Thermochemical reaction
    • Combustion reaction
    Answer & explanation

    Correct: Endothermic reaction

    An endothermic reaction absorbs heat from the surroundings.

13. 13. What type of respiration requires oxygen?

    • Anaerobic respiration
    • Aerobic respiration
    • Oxidative respiration
    • Fermentation
    Answer & explanation

    Correct: Aerobic respiration

    Aerobic respiration is the type that requires oxygen to break down glucose for energy.

14. 14. What does catalysis refer to?

    • The process of using a catalyst to accelerate a reaction.
    • The process of creating a new product.
    • The measurement of reaction rates.
    • The calculation of enthalpy changes.
    Answer & explanation

    Correct: The process of using a catalyst to accelerate a reaction.

    Catalysis is the phenomenon where a catalyst is used to accelerate a chemical reaction.

15. 15. What happens if the energy of the reacting particles is lower than the activation energy?

    • A chemical reaction cannot occur
    • The reaction rate increases
    • It results in complete bond formation
    • The particles explode
    Answer & explanation

    Correct: A chemical reaction cannot occur

    If the energy of the reacting particles is lower than the activation energy, no reaction occurs.

16. 16. What indicates whether a reaction absorbs or releases energy?

    • The bond dissociation energy and bond energy difference
    • The temperature of the reaction
    • The concentration of reactants
    • The phase of the reactants
    Answer & explanation

    Correct: The bond dissociation energy and bond energy difference

    The difference between the bond dissociation energy and the bond energy determines whether the reaction absorbs or releases energy.

17. 17. When does a net release of chemical energy occur?

    • When no energy is exchanged.
    • When energy released is greater than energy consumed.
    • When energy consumed is greater than energy released.
    • When bonds are not formed.
    Answer & explanation

    Correct: When energy released is greater than energy consumed.

    A net release of chemical energy occurs when the energy released in forming a bond is greater than the energy expended in breaking the bond.

18. 18. What term is used for the enthalpy of reaction measured at 25°C and one atmospheric pressure?

    • Standard enthalpy change
    • Specific enthalpy
    • Variable enthalpy
    • Normal enthalpy
    Answer & explanation

    Correct: Standard enthalpy change

    The enthalpy of reaction measured at 25°C and one atmospheric pressure is known as standard enthalpy change.

19. 19. What does a thermochemical equation show?

    • Only the products of a reaction
    • The heat change of a chemical reaction
    • The temperature of the reactants
    • The total mass of the system
    Answer & explanation

    Correct: The heat change of a chemical reaction

    A thermochemical equation shows the heat change associated with a chemical reaction.

20. 20. During aerobic respiration, glucose is converted to which products?

    • Carbon dioxide and water
    • Oxygen and lactic acid
    • Carbon monoxide and water
    • Starch and energy
    Answer & explanation

    Correct: Carbon dioxide and water

    Aerobic respiration converts glucose and oxygen into carbon dioxide, water, and energy.

21. 21. How does a catalyst increase the rate of a reaction?

    • By lowering the activation energy.
    • By increasing the temperature of the reactants.
    • By changing the products of the reaction.
    • By consuming reactants during the process.
    Answer & explanation

    Correct: By lowering the activation energy.

    A catalyst increases the rate of a reaction by providing a new mechanism with lower activation energy.

22. 22. How does activation energy affect the reaction rate?

    • Higher activation energy results in a lower reaction rate
    • Lower activation energy results in a slower reaction rate
    • Activation energy does not affect reaction rate
    • Higher activation energy increases the reaction rate
    Answer & explanation

    Correct: Higher activation energy results in a lower reaction rate

    The higher the activation energy, the lower the reaction rate.

23. 23. What is the enthalpy change in a chemical reaction represented by?

    • ΔH° = Sum of bond energies of reactants + Sum of bond dissociation energies of products
    • ΔH° = Sum of bond dissociation energies of reactants - Sum of bond energies of products
    • ΔH° = Sum of energies absorbed only
    • ΔH° = Sum of energies released only
    Answer & explanation

    Correct: ΔH° = Sum of bond dissociation energies of reactants - Sum of bond energies of products

    The enthalpy change is represented by ΔH° = Sum of bond dissociation energies of reactants - Sum of bond energies of products.

24. 24. What defines the system in a chemical reaction?

    • The entire universe.
    • The part of the universe focused on in the study.
    • Only the products of a reaction.
    • Only the reactants involved.
    Answer & explanation

    Correct: The part of the universe focused on in the study.

    The system is defined as the part of the universe that we want to focus our attention on, typically a substance changing physically or chemically.

25. 25. How is standard enthalpy change denoted?

    • ΔH°
    • ΔH
    • ΔE
    • ΔS
    Answer & explanation

    Correct: ΔH°

    Standard enthalpy change is denoted by ΔH°.