LT 33: multi-step energy profiles, catalysts

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 (hold) one of the particles, making a successful (reaction-producing) collision with the other particle more likely

Tags

NGSS.HS-PS1-5

The energy diagram for the reaction X + Y  --> Z is shown.  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

Tags

NGSS.HS-PS1-4

The energy diagram for the reaction X + Y  --> Z is shown.  At what point on the graph is the activated complex present?

• A

• B

• C

• D

Tags

NGSS.HS-PS1-4

The energy diagram for the reaction X + Y  --> Z is shown.  What would happen if the kinetic energy of the reactants was not enough to provide the needed activation energy?

• The rate of the reaction would tend to increase

• The activated complex would convert into products

• The reactants would continue to exist in their present state

• The products would form at an unstable energy state

Tags

NGSS.HS-PS1-4

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Tags

NGSS.HS-PS1-4

O₃(g) + O(g)  →  2O₂(g)

The decomposition of O₃(g) in the upper atmosphere is represented by the equation above.  The potential energy diagram for the decomposition of O₃(g) in the presence and absence of NO(g) is given below. Which of the following mechanisms for the catalyzed reaction is consistent with the equation and diagram above?

• 2O₃(g)  +  2NO(g) →  4O₂(g)  +  N₂(g) (slow) 

• O₃(g) + NO(g)→  NO₂(g) + O₂(g) (slow)

  NO₂(g) + O(g) → NO(g) + O₂(g) (fast)

• NO₂(g) + O₃(g) → NO(g) + 2O₂(g) (slow)

  NO(g)  +  O(g)  → NO₂(g)  (fast)

• NO₂(g) + O(g) → NO₃(g)  (slow)

  NO₃(g) + O₃(g)→ NO₂(g) + 2O₂(g) (fast)

Tags

NGSS.HS-PS1-4

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 H atoms to form new H-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)

Tags

NGSS.HS-PS1-4

The energy distribution profile (Curve C) for the Y₂ molecules is shown in the graph for the reaction  X + Y₂ --> XY₂ when it is done under certain experimental conditions.  Line A represents the most probably 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

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

A reaction profile shows....

• the relative difference in temperature of reactants and products

• the relative difference in amounts of reactants and products

• the relative difference in energy of reactants and products

• the relative difference in volume of reactants and products

Tags

NGSS.HS-PS1-4

The minimum energy particles must have to react is the

• acting energy

• active energy

• activation energy