Catalysts Knowledge-Based Download PDF

Questions

1. 1.

   According to the Maxwell-Boltzmann distribution of molecular energies, how does the addition of a catalyst affect a reaction mixture at constant temperature?

   • A) It increases the average kinetic energy of the reacting molecules.
   • B) It broadens the molecular energy distribution curve by increasing the total collision frequency.
   • C) It leaves the molecular energy distribution curve unchanged while lowering the threshold energy required for effective collisions.
   • D) It shifts the peak of the molecular energy distribution curve toward higher kinetic energy values.
2. 2.

   In heterogeneous catalysis, which of the following statements best describes the primary chemical function of chemisorption on the catalyst surface?

   • A) It binds reactant molecules to active sites and weakens specific internal chemical bonds, facilitating subsequent reaction steps.
   • B) It permanently incorporates reactant molecules into the bulk solid lattice to form an irreversible stoichiometric compound.
   • C) It significantly raises the kinetic energy of surrounding gas-phase molecules by converting surface potential energy into heat.
   • D) It increases the net enthalpy change of the reaction, making the conversion from reactants to products more exothermic.
3. 3.

   Which of the following properties of a chemical reaction is directly altered by the addition of a catalyst?

   • A) The standard enthalpy change ($\Delta H^\circ$) of the overall reaction
   • B) The activation energy ($E_{\text{a}}$) required to reach the transition state
   • C) The internal potential energy of the ground-state reactant molecules
   • D) The standard Gibbs free energy change ($\Delta G^\circ$) of the overall reaction
4. 4.

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

   • A) A catalyst is generated as a product in an early elementary step and consumed in a later step, whereas an intermediate is consumed first and regenerated later.
   • B) A catalyst is consumed as a reactant in an early elementary step and regenerated in a later step, whereas an intermediate is produced first and consumed later.
   • C) A catalyst appears in the stoichiometric equation of the overall reaction, whereas an intermediate does not appear in the overall balanced equation.
   • D) A catalyst alters the standard enthalpy change of the overall reaction, whereas an intermediate only affects the activation energy of the elementary steps.
5. 5.

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

   • A) It shifts the equilibrium toward the products, resulting in a higher equilibrium yield.
   • B) It provides an alternative reaction pathway with a lower activation energy, increasing the rates of both the forward and reverse reactions equally.
   • C) It decreases the overall enthalpy change of the reaction, making the process more thermodynamically favorable.
   • D) It increases the average kinetic energy of the reacting particles, leading to more frequent collisions.