5.5 Introduction to Reaction Mechanisms

• An elementary step involves the formation or breakage of a single bond.


  True
• Molecularity refers to the exponents in the rate law of a reaction.

  False
• Reaction intermediates differ from catalysts because catalysts are not consumed
• A reaction mechanism represents the net stoichiometry of a reaction.

  False
• Steps in the reaction mechanism for 2NO(g) + O₂(g) → 2NO₂(g)

  1️⃣ NO(g) + O₂(g) → NO₃(g)

  2️⃣ NO₃(g) + NO(g) → 2NO₂(g)
• Match the feature with the correct description:

  Elementary Step ↔️ Single step occurrence

  Overall Reaction ↔️ Multi-step occurrence
• Molecularity values are typically 1, 2, or 3
• Reaction intermediates are always consumed in a reaction mechanism.


  True
• A reaction mechanism consists of individual steps called elementary
• In the reaction `NO(g) + O₂(g) → NO₃(g)`, a new bond between N and O is formed
• Reaction intermediates are consumed during the reaction mechanism.


  True
• What is a reaction mechanism composed of?

  Elementary reactions
• The reaction mechanism for 2NO(g) + O₂(g) → 2NO₂(g) consists of two elementary steps
• Elementary steps represent specific bond changes
• The order of a reaction is determined experimentally.


  True
• What is a reaction intermediate?

  Transient species formed and consumed
• What is the key difference between unimolecular and bimolecular steps?

  Number of reactant molecules
• Arrange the key characteristics of elementary steps:

  1️⃣ Occur in a single step

  2️⃣ Represent specific bond changes

  3️⃣ Have a well-defined rate law

  4️⃣ Can involve intermediates
• In the reaction `2NO(g) + O₂(g) → 2NO₂(g)`, the molecularity of the first step is two
• Arrange the steps in the given reaction mechanism to identify the intermediate:

  1️⃣ A → B

  2️⃣ B + C → D
• What does a reaction mechanism show that a balanced equation does not?

  Intermediates and transition states
• What does an elementary step represent in a reaction mechanism?

  Single bond changes
• What is the molecularity of the elementary step NO(g) + O₂(g) → NO₃(g)?

  2
• What is the experimental rate law for the reaction 2NO(g) + O₂(g) → 2NO₂(g) if its elementary steps are NO(g) + O₂(g) → NO₃(g) and NO₃(g) + NO(g) → 2NO₂(g)?

  $k[NO]^{2}[O₂]$
• Catalysts accelerate reactions but are not consumed
• Match the feature with the correct type of substance:

  Catalyst ↔️ Accelerates reaction, regenerated

  Reaction Intermediate ↔️ Transient species formed and consumed
• A catalyst increases the reaction rate without being consumed in the process.


  True