AP 5.11 Catalysis BANK

The energy diagram for the reaction X + Y → Z is shown above. The addition of a catalyst to this reaction would cause a change in which of the indicated energy differences?

• I only

• II only

• III only

• I and II only

• I, II, and III

The energy distribution profile (Curve C) for the Y2 molecules is shown in the graph above for the reaction X+Y2→XY2 when it is done under certain experimental conditions. Line A represents the most probable energy of the Y2 molecules, and Line B represents the activation energy. Which of the following changes should be made to the graph to explain the increase in the rate of the reaction if the only change in experimental conditions is the addition of a catalyst?

• Curve C will broaden and Line B will move to the left, because more Y2 molecules will have an energy greater than the minimum energy needed to overcome the activation energy barrier.

• Line B will move to the left because a larger fraction of the Y2 molecules will have the minimum energy to overcome the activation energy barrier.

• Curve C and Line A will move to the right because the average energy of the Y2 molecules will increase.

• Line A will move to the right because the most probable energy of the Y2 molecules will increase.

The slowest step in a reaction mechanism requires the collision represented above to occur. Which of the following most likely indicates how the addition of a solid catalyst could increase the rate of the reaction?

• The catalyst could change the reaction from second order to third order.

• The catalyst could increase the particles’ speed, thereby increasing the value of the rate constant, k.

• The catalyst could decrease the particles’ speed, making it less likely that the particles will rebound without reacting when they collide.

• The catalyst could adsorb one of the particles, making a successful (reaction-producing) collision with the other particle more likely.

To catalyze a biochemical reaction, an enzyme typically

• drives the reaction to completion by consuming byproducts of the reaction

• binds temporarily to reactant molecules to lower the activation energy of the reaction

• dissociates into additional reactant molecules, thereby increasing the reaction rate

• decomposes and releases energy to increase the number of successful collisions between reactant molecules

N₂O(g) + CO(g) → N₂(g) + CO₂(g)

The rate of the reaction represented above increases significantly in the presence of Pd(s). Which of the following best explains this observation?

• Pd increases the activation energy of the reaction.

• Pd absorbs the heat produced in the reaction.

• One of the reactants binds on the surface of Pd, which introduces an alternative reaction pathway with a lower activation energy.

• One of the products binds on the surface of Pd, which increases the reaction rate by decreasing the concentration of products in the mixture.

The diagram above illustrates how the reaction N2(g)+3H2(g)→2NH3(g) occurs on the surface of Ru(s). The rate of this reaction is determined by the amount of energy required to break the bond in N2. This bond is weakened when N2 is adsorbed on Ru(s). Based on this information, which of the following provides the best reason for the use of Ru(s) for the synthesis of NH3 ?

• It promotes the proper orientation of N and HH atoms to form new N−H bonds.

• It provides a reaction path with a lower activation energy.

• It forms a bond between Ru and N that is stronger than the bond in N2.

• It decreases the frequency of collisions between N2(g) and H2(g).

The following questions relate to the below information.

XY₂ → X + Y₂

The equation above represents the decomposition of a compound XY₂. The diagram below shows two reaction profiles (path one and path two) for the decomposition of XY₂.

Which of the following most likely accounts for the difference between reaction path one and reaction path two?

• A higher temperature in path one

• A higher temperature in path two

• The presence of a catalyst in path one

• The presence of a catalyst in path two

The hydrolysis of sucrose is represented by the chemical equation above. This reaction is extremely slow in aqueous solution. However, when sucrase is added as shown in the diagram, the rate of the reaction is about 6,000,000 times faster. Based on this information, which of the following best explains the large increase in the rate of hydrolysis that occurs with the addition of sucrase?

• The reaction proceeds through a different reaction path with a lower activation energy in which the sucrase-sucrose complex is formed as an intermediate.

• The addition of the sucrase reduces the number of effective collisions between the water and sucrose molecules.

• The reaction proceeds through a different reaction path that is independent of temperature and concentration.

• The addition of the sucrase decreases the number of sucrose molecules that have the minimum energy required to overcome the activation energy barrier.

The role of a catalyst in a chemical reaction is to

• decrease the amount of reactants that must be used

• lower the activation energy for the reaction

• supply the activation energy required for the reaction to proceed

• increase the amounts of products formed at equilibrium

• increase the entropy change for the reaction

Catalysts may be in the state of ___________.

• Solid and liquid only

• Liquid and gases only

• Solid and gases only

• Solid, liquid or gases