Questions on Activation Energy and Activated Complex
Multiple-Choice Questions: Activation Energy and Activated Complex
1. What is activation energy?
A) Energy stored in the products
B) Energy required to start a nuclear reaction
C) Minimum energy required for a chemical reaction to occur
D) Energy absorbed by the surroundings during a reaction
E) The energy of the final state of the system
2. What does the term "activated complex" refer to?
A) A stable product of a chemical reaction
B) A set of slow-reacting molecules
C) A temporary high-energy state formed during a reaction
D) A solid catalyst involved in the reaction
E) A buffer added to stabilize the reactants
3. Where does the activated complex appear on an energy diagram?
A) At the energy level of the products
B) At the midpoint between products and reactants
C) At the peak of the energy curve
D) Below the reactants' energy level
E) Just before the products
4. What is another common name for the activated complex?
A) Reaction product
B) Reaction catalyst
C) Transition state
D) Reaction barrier
E) Initial compound
5. Which of the following statements is true about the activated complex?
A) It is always lower in energy than the reactants
B) It is a stable compound
C) It exists briefly and can form either products or revert to reactants
D) It has the same energy as the products
E) It only forms in exothermic reactions
6. Which of the following best describes the function of activation energy?
A) It determines the color of the product
B) It is the energy needed to break bonds in the reactants
C) It maintains the stability of the products
D) It cools the reaction mixture
E) It acts as a catalyst
7. What happens to the number of particles that form an activated complex as temperature increases?
A) It decreases
B) It stays the same
C) It increases
D) It becomes zero
E) It fluctuates randomly
8. How does a catalyst affect the activation energy of a reaction?
A) Increases it
B) Decreases it
C) Eliminates it completely
D) Converts it into kinetic energy
E) Raises the energy of the products
9. Which of the following is true about a reaction with a high activation energy?
A) It always proceeds rapidly
B) It is spontaneous
C) It occurs slowly without a catalyst
D) It does not form an activated complex
E) It occurs faster at low temperatures
10. What is the fate of the activated complex in a chemical reaction?
A) It always breaks down into products
B) It always returns to reactants
C) It may form products or revert to reactants
D) It forms new reactants
E) It becomes a catalyst
11. Which equation includes activation energy as a variable?
A) Ideal gas law
B) Arrhenius equation
C) Boyle’s law
D) Dalton’s law
E) Charles’s law
12. In the Arrhenius equation, what does ‘Ea’ represent?
A) The energy of the products
B) Activation energy
C) Energy of equilibrium
D) Energy capacity
E) Energy lost as heat
13. Why does lowering activation energy increase the rate of a chemical reaction?
A) It increases the mass of the particles
B) More particles can overcome the energy barrier
C) The products are more stable
D) It increases the volume of the reactants
E) It decreases the entropy of the system
14. What does the activated complex represent in terms of bond structure?
A) Fully broken bonds in reactants
B) Fully formed bonds in products
C) A partial breaking and forming of bonds
D) The original bond configuration
E) No bond changes
15. Which energy state has the highest potential energy in a reaction coordinate diagram?
A) Reactants
B) Products
C) Intermediates
D) Activated complex
E) Catalyst
16. Which statement best describes the relationship between activation energy and temperature?
A) Activation energy increases with temperature
B) Activation energy is eliminated at higher temperatures
C) Higher temperature allows more particles to overcome activation energy
D) Temperature and activation energy are unrelated
E) Temperature only affects the products
17. What is the significance of the peak of a reaction energy diagram?
A) It shows the stability of the reactants
B) It represents the catalyst
C) It indicates the activated complex and activation energy
D) It is the equilibrium point
E) It shows the bond length of products
18. Which condition would favor the formation of the activated complex?
A) Low kinetic energy
B) Low temperature
C) High frequency of effective collisions
D) Zero activation energy
E) Product removal
19. How does activation energy differ between exothermic and endothermic reactions?
A) It is lower for exothermic reactions
B) It is only needed for endothermic reactions
C) It is negative in exothermic reactions
D) It is the same for both
E) It does not apply to endothermic reactions
20. Which of the following is NOT true about the activated complex?
A) It is a transitional structure
B) It is highly unstable
C) It exists momentarily
D) It has lower energy than the reactants
E) It can lead to product formation
Answer Key with Explanations
1. C – Activation energy is the minimum energy required for a chemical reaction to start.
2. C – The activated complex is the temporary high-energy arrangement during a reaction.
3. C – On an energy diagram, the activated complex appears at the peak.
4. C – Another name for the activated complex is the transition state.
5. C – The activated complex is unstable and can either proceed to products or revert to reactants.
6. B – Activation energy is required to break bonds and initiate the reaction.
7. C – As temperature increases, more particles have energy ≥ Ea, so more reach the activated complex.
8. B – Catalysts lower the activation energy, allowing the reaction to proceed more easily.
9. C – A reaction with high activation energy typically proceeds slowly unless a catalyst is present.
10. C – The activated complex may form products or revert to reactants.
11. B – The Arrhenius equation relates rate constant to activation energy and temperature.
12. B – ‘Ea’ stands for activation energy in the Arrhenius equation.
13. B – Lower Ea means more particles can successfully react, increasing reaction rate.
14. C – The activated complex is a partially bonded state—bonds are forming and breaking.
15. D – The activated complex has the highest energy in the reaction pathway.
16. C – Higher temperature increases the fraction of particles with energy ≥ Ea.
17. C – The peak of the energy diagram represents the transition state (activated complex) and Ea.
18. C – Effective collisions with sufficient energy and correct orientation favor activated complex formation.
19. A – Generally, exothermic reactions require lower activation energy.
20. D – The activated complex has higher energy than both reactants and products.
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