5.3 Elementary Reactions

• Complex reactions involve multiple steps
• The unimolecular reaction example is N_2O_5(g)
• What are elementary reactions characterized by?

  Single-step reactions
• The rate law for a complex reaction can be determined directly from its stoichiometry.

  False
• Complex reactions involve multiple steps.
• What type of molecularity involves a single molecule as a reactant?

  Unimolecular
• The termolecular reaction \(2NO(g) + O_2(g) \rightarrow 2NO_2(g)\) involves three molecules.
• The rate law for an elementary step is determined by its stoichiometry.
• How is the rate law for an elementary reaction determined?

  From stoichiometry
• Why can the rate law for elementary reactions be determined directly from stoichiometry?

  They occur in a single step
• The rate law for a termolecular reaction \(2A + B \rightarrow Products\) is \(Rate = k[A]^2[B]\)


  True
• Why must the rate laws for complex reactions be determined experimentally?

  They involve multiple steps
• Elementary reactions are chemical reactions that occur in a single step
• For the elementary reaction \(2NO(g) + O_2(g) \rightarrow 2NO_2(g)\), the rate law is Rate = k[NO]^2[O_2]
• What does molecularity refer to in an elementary reaction?

  Number of reactant molecules
• What are the three types of molecularity in elementary reactions?

  Unimolecular, bimolecular, termolecular
• Reaction mechanisms describe the detailed sequence of elementary steps in a chemical reaction.


  True
• The rate-determining step in a reaction mechanism is the slowest
• Steps in the reaction mechanism for \(2O_3(g) \rightarrow 3O_2(g)\)

  1️⃣ \(2O_3(g) \rightarrow 3O_2(g) + O(g)\) (Slow)

  2️⃣ \(O(g) + O_3(g) \rightarrow 2O_2(g)\) (Fast)
• Match the molecularity of an elementary reaction with its rate law:

  Unimolecular ↔️ Rate = k[A]</latex>

  Bimolecular ↔️ $Rate =$$k[A][B]$

  Termolecular ↔️ $Rate =$$k[A]^{2}[B]$
• The minimum energy required for a reaction to occur is called the activation
• Elementary reactions occur in a single step
• Complex reactions require experimental data to determine their rate laws.


  True
• Molecularity refers to the number of molecules that participate as reactants in an elementary reaction.
• A termolecular reaction involves three molecules as reactants.


  True
• Elementary reactions occur in a single step.
• Match the feature with the type of reaction:

  Single step ↔️ Elementary reaction

  Multiple steps ↔️ Complex reaction
• The rate law for \(2NO(g) + O_2(g) \rightarrow 2NO_2(g)\) is \(Rate = k[NO]^2[O_2]\).


  True
• What is an example of a unimolecular reaction?

  \(N_2O_5(g) \rightarrow 2NO_2(g) + \frac{1}{2}O_2(g)\)
• What is the role of the rate-determining step in a reaction mechanism?

  Controls overall reaction rate
• Arrange the steps in the reaction mechanism for \(2O_3(g) \rightarrow 3O_2(g)\):

  1️⃣ \(O_3(g) \rightarrow O_2(g) + O(g)\) (Slow)

  2️⃣ \(O(g) + O_3(g) \rightarrow 2O_2(g)\) (Fast)
• Match the molecularity with its corresponding rate law:

  Unimolecular ↔️ \(Rate = k[A]\)

  Bimolecular ↔️ \(Rate = k[A][B]\)

  Termolecular ↔️ \(Rate = k[A]^2[B]\)
• What is the rate law for a bimolecular reaction involving reactants A and B?

  Rate = k[A][B]
• Elementary reactions occur in a single step
• The rate law for an elementary reaction can be determined from its stoichiometry.

  True
• Match the type of reaction with its method of rate law determination:

  Elementary Reaction ↔️ Directly from stoichiometry

  Complex Reaction ↔️ Experimental data
• Complex reactions require experimental data to determine their rate laws.

  True
• In a unimolecular reaction, a single molecule decomposes to form products.
• What is the rate-determining step in a reaction mechanism?

  The slowest step
• How is the rate law determined for a complex reaction?

  Experimental data