16.3.1 Determining Mechanisms

• What is a reaction mechanism?

  Step-by-step reaction description
• The reaction between NO2 and CO to form NO and CO2 occurs through a single-step mechanism.

  False
• The slowest step in a reaction mechanism is called the rate-determining step.
• What is an elementary reaction?

  Single-step reaction process
• An elementary reaction involves intermediate steps.

  False
• The rate-determining step is the slowest step in a reaction mechanism.
• What is the reaction rate proportional to if the first step of the NO2 and CO reaction is the RDS?

  $[NO_{2}]^{2}$
• Steps to propose potential reaction mechanisms

  1️⃣ Write down the overall reaction

  2️⃣ Consider elementary steps

  3️⃣ Identify intermediates

  4️⃣ Check mass and charge balance

  5️⃣ Compare with experimental data
• To validate a proposed mechanism, compare its predicted rate law with the experimentally determined rate law.
• What are reaction intermediates?

  Short-lived species in mechanisms
• Reaction intermediates appear in the overall reaction equation.

  False
• What are the two key characteristics of a catalyst in a reaction mechanism?

  Used and regenerated
• What role does NO2 play in the reaction between NO2 and CO according to the study material?

  Not a catalyst
• A catalyst is a substance that speeds up a chemical reaction without being consumed
• A catalyst must be regenerated in another step to be identified in a reaction mechanism.
• What is a reaction mechanism in chemistry?

  Sequence of elementary steps
• Steps in the reaction mechanism between NO2 and CO

  1️⃣ NO_{2} + NO_{2} \rightarrow NO + NO_{3}

  2️⃣ NO_{3} + CO \rightarrow NO_{2} + CO_{2}
• An elementary reaction is a single-step process without intermediate steps
• Match the type of elementary reaction with its description:

  Unimolecular ↔️ Single molecule decomposes

  Bimolecular ↔️ Two molecules collide
• The rate-determining step is always the fastest step in a reaction mechanism.

  False
• What is the rate law for the reaction NO2 + CO if the rate-determining step is 2NO2 → NO + NO3?

  rate = k[NO_{2}]^{2}</latex>
• To propose a reaction mechanism, the first step is to write down the overall reaction
• What does the Arrhenius equation describe?

  Temperature effects on rate
• Reaction intermediates appear in the overall reaction equation.

  False
• A catalyst lowers the activation energy
• Match the type of catalyst with its description:

  Homogeneous ↔️ Same phase as reactants

  Heterogeneous ↔️ Different phase from reactants
• What is the rate law for the reaction NO2 + CO if the rate-determining step is 2NO2 → NO + NO3?

  $rate =$$k[NO_{2}]^{2}$
• Molecularity refers to the number of reactant molecules in an elementary reaction
• Order the types of molecularity from highest to lowest frequency:

  1️⃣ Bimolecular

  2️⃣ Unimolecular

  3️⃣ Trimolecular
• Trimolecular reactions are less common due to the low probability of three molecules colliding simultaneously.