Reaction Mechanisms MCQs

1. What is the term for a sequence of elementary steps that describes the detailed process of a chemical reaction? a) Reaction pathway b) Reaction mechanism c) Reaction coordinate d) Rate law Answer: b) Reaction mechanism 2. In a reaction mechanism, what is an intermediate? a) A reactant that is consumed during the reaction b) A product that is formed in the reaction c) A substance that is neither a reactant nor a product but is formed and consumed during the reaction d) The final product of the reaction Answer: c) A substance that is neither a reactant nor a product but is formed and consumed during the reaction 3. What is the term for a step in a reaction mechanism that is the slowest and determines the overall reaction rate? a) Rate-determining step b) Fast step c) Intermediate step d) Equilibrium step Answer: a) Rate-determining step 4. How does a catalyst affect the reaction mechanism? a) It changes the overall reaction balance b) It increases the activation energy of the reaction c) It lowers the activation energy of the reaction and provides an alternative pathway d) It decreases the concentration of reactants Answer: c) It lowers the activation energy of the reaction and provides an alternative pathway 5. What is the term for a proposed series of steps that must occur for a reaction to proceed from reactants to products? a) Reaction pathway b) Reaction mechanism c) Reaction order d) Transition state Answer: b) Reaction mechanism 6. In a reaction mechanism, what is a transition state? a) The state of a reactant before the reaction begins b) A high-energy, unstable state through which reactants must pass to form products c) The state of the final product of the reaction d) The equilibrium state of the reactants and products Answer: b) A high-energy, unstable state through which reactants must pass to form products 7. What is the term for the species that is formed in one elementary step and consumed in a subsequent step? a) Reactant b) Intermediate c) Catalyst d) Product Answer: b) Intermediate 8. Which of the following best describes the overall reaction rate when a reaction mechanism has multiple steps? a) It is determined by the rate of the fastest step b) It is determined by the rate of the slowest step c) It is the average rate of all steps combined d) It is not affected by the mechanism Answer: b) It is determined by the rate of the slowest step 9. What does the term “elementary step” refer to in a reaction mechanism? a) A step involving multiple molecules b) A step that is the overall reaction c) A single molecular event that occurs in the mechanism d) A step that occurs at equilibrium Answer: c) A single molecular event that occurs in the mechanism 10. How can the reaction mechanism be inferred from experimental data? a) By measuring the total energy of the reaction b) By analyzing the rates of reaction and the effect of different conditions c) By observing the physical appearance of the reactants and products d) By calculating the equilibrium constant Answer: b) By analyzing the rates of reaction and the effect of different conditions 11. What is the term for a reaction that involves a sequence of two or more elementary steps? a) Unimolecular reaction b) Bimolecular reaction c) Chain reaction d) Complex reaction Answer: d) Complex reaction 12. Which of the following statements is true about intermediates in a reaction mechanism? a) They are present in the initial state and are consumed by the end of the reaction b) They are always detectable in the final products c) They are usually formed in the final step of the reaction d) They are stable, long-lived species Answer: a) They are present in the initial state and are consumed by the end of the reaction 13. What role does a catalyst play in the reaction mechanism? a) It changes the equilibrium position of the reaction b) It shifts the reaction to favor the products c) It lowers the activation energy and speeds up the reaction d) It increases the concentration of the reactants Answer: c) It lowers the activation energy and speeds up the reaction 14. What is the term for the series of elementary steps that leads to the formation of the final product? a) Reaction path b) Reaction coordinate c) Reaction mechanism d) Rate law Answer: a) Reaction path 15. What is the term for the highest energy state along the reaction path, which corresponds to the transition state? a) Activation energy b) Reaction intermediate c) Transition state d) Reactant state Answer: c) Transition state 16. How is the rate-determining step identified in a reaction mechanism? a) By its highest energy barrier b) By its lowest energy barrier c) By its rate constant d) By its equilibrium constant Answer: a) By its highest energy barrier 17. What is a key feature of a chain reaction mechanism? a) It involves a single elementary step b) It has a series of steps where each step generates a new reactant c) It does not involve any intermediates d) It is always an endothermic process Answer: b) It has a series of steps where each step generates a new reactant 18. What does the term “reaction pathway” refer to? a) The path taken by reactants to become products b) The route by which intermediates are formed c) The series of elementary steps from reactants to products d) The final equilibrium state of the reaction Answer: c) The series of elementary steps from reactants to products 19. What information does a reaction coordinate diagram provide? a) The concentration of reactants and products at equilibrium b) The time taken for the reaction to reach completion c) The energy changes throughout the reaction mechanism d) The temperature at which the reaction occurs Answer: c) The energy changes throughout the reaction mechanism 20. Which of the following factors can affect the rate-determining step of a reaction? a) Temperature b) Pressure c) Concentration of reactants d) All of the above Answer: d) All of the above 21. In a reaction mechanism, what is a “chain reaction”? a) A reaction where intermediates are formed but not consumed b) A reaction involving a single elementary step c) A reaction where each step produces a new reactant that continues the chain d) A reaction where all products are formed at once Answer: c) A reaction where each step produces a new reactant that continues the chain 22. What term describes the process where a reactant forms a product in a series of steps, each with its own transition state? a) Sequential reaction b) Multi-step reaction c) Single-step reaction d) Isomeric reaction Answer: b) Multi-step reaction 23. What is the main purpose of studying a reaction mechanism? a) To determine the final product only b) To understand the detailed process and rate of reaction c) To find the equilibrium constant d) To calculate the reaction yield Answer: b) To understand the detailed process and rate of reaction 24. How does the presence of a catalyst affect the reaction mechanism? a) It changes the products formed b) It provides an alternative reaction pathway with a lower activation energy c) It alters the reaction equilibrium d) It increases the activation energy required Answer: b) It provides an alternative reaction pathway with a lower activation energy 25. In a reaction mechanism, what is the role of the “slow step”? a) It is the step that produces the most intermediate b) It is the fastest step in the mechanism c) It is the step that controls the overall reaction rate d) It is the step with the lowest activation energy Answer: c) It is the step that controls the overall reaction rate 26. What does a “reaction rate law” express? a) The relationship between the concentration of reactants and the reaction rate b) The energy changes during the reaction c) The steps involved in the reaction mechanism d) The temperature dependence of the reaction Answer: a) The relationship between the concentration of reactants and the reaction rate 27. What term describes the step in a reaction mechanism where reactants are transformed into products? a) Elementary step b) Rate-determining step c) Intermediate step d) Chain step Answer: a) Elementary step 28. What is a characteristic feature of a reaction mechanism involving a multi-step process? a) The overall reaction is the sum of all elementary steps b) The rate of the reaction is constant throughout all steps c) The intermediate species are always present in the final product d) The reaction does not proceed through any transition states Answer: a) The overall reaction is the sum of all elementary steps 29. How can the experimental observation of reaction intermediates be useful in studying reaction mechanisms? a) It helps determine the overall reaction equilibrium b) It provides insight into the specific steps of the reaction mechanism c) It measures the rate of the reaction d) It calculates the final product yield Answer: b) It provides insight into the specific steps of the reaction mechanism 30. What is the main goal of proposing a reaction mechanism? a) To predict the color of the reaction b) To understand the detailed sequence of events that occur during the reaction c) To determine the volume of reactants used d) To calculate the energy released Answer: b) To understand the detailed sequence of events that occur during the reaction