Catalysts Knowledge-Based Practice

Questions

1. 1.

   Which of the following values remains completely unchanged when a chemical reaction proceeds via a catalyzed pathway rather than an uncatalyzed pathway?

   • A) The activation energy of the reverse reaction
   • B) The rate constant of the forward reaction
   • C) The net enthalpy change ($\Delta H$) of the reaction
   • D) The chemical nature of the transition state
2. 2.

   Which of the following statements correctly distinguishes a heterogeneous catalyst from a homogeneous catalyst in chemical kinetics?

   • A) A heterogeneous catalyst exists in a different physical phase from the reactants, whereas a homogeneous catalyst exists in the same phase as the reactants.
   • B) A heterogeneous catalyst alters the overall standard enthalpy change of the reaction, whereas a homogeneous catalyst leaves it unchanged.
   • C) A heterogeneous catalyst is consumed during the reaction without being regenerated, whereas a homogeneous catalyst is fully regenerated.
   • D) A heterogeneous catalyst accelerates only the forward pathway, whereas a homogeneous catalyst accelerates both forward and reverse pathways.
3. 3.

   Which of the following statements correctly explains how the addition of a catalyst increases the rate of a chemical reaction at a constant temperature?

   • A) It increases the average kinetic energy of the colliding reactant molecules.
   • B) It provides an alternative reaction pathway characterized by a lower activation energy.
   • C) It increases the total collision frequency between reactant particles.
   • D) It makes the overall reaction more exothermic by lowering the potential energy of the products.
4. 4.

   In a multistep chemical reaction mechanism, how is a catalyst distinguished from a reaction intermediate?

   • A) A catalyst is generated as a product in an early elementary step and consumed in a subsequent step.
   • B) A catalyst appears in the balanced overall chemical equation, whereas a reaction intermediate does not.
   • C) A catalyst increases the activation energy of the rate-determining step to stabilize unstable intermediates.
   • D) A catalyst is consumed as a reactant in an early elementary step and regenerated in a subsequent step.
5. 5.

   Which of the following statements correctly describes the effect of a catalyst on a reversible chemical reaction?

   • A) It increases the equilibrium yield of products by shifting the equilibrium toward the forward direction.
   • B) It lowers the activation energy of both the forward and reverse reactions by providing an alternative mechanism.
   • C) It increases the reaction rate by increasing the average kinetic energy of the reacting particles.
   • D) It decreases the overall enthalpy change of the reaction to make the forward process more exothermic.

Answers and step-by-step solutions appear after you finish the test.