Chemistry Lecture 13: Rate Limiting Steps

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Questions and Answers

What are the reaction intermediates in the provided series of elementary steps?

HOI and OH- (correct)

Cl- and HOI (correct)

OCl- and HOCl

I- and CO2

Which step in the provided reaction series is likely to be the rate determining step?

The second step involving I- and HOCl (correct)

The first step involving OCl- and H2O

The third step involving OH- and HOI

There is no rate limiting step

Based on the identified rate limiting step, which rate law can be proposed?

Rate = k[OCl-][H2O]

Rate = k[Cl-][I-]

Rate = k[I-][HOCl] (correct)

Rate = k[OH-][HOI]

In the series of elementary steps, which of the following represents an elementary reaction?

OCl- (aq) + H2O (l) → HOCl (aq) + OH- (aq) Signup and view all the answers

What role does water play in the elementary steps involving OCl-?

It is a reactant Signup and view all the answers

What is the overall reaction represented in the provided content?

NO2(g) + CO(g) → NO(g) + CO2(g) Signup and view all the answers

What is the molecularity of the rate law for step 1 in the provided reaction mechanisms?

Bimolecular Signup and view all the answers

Which expression correctly represents the rate law for step 2 of the reaction?

Rate = k[NO3][CO] Signup and view all the answers

What does the term 'reaction mechanism' refer to in the context of chemical reactions?

The sequence of elementary steps leading to products Signup and view all the answers

In the provided context, which elementary step is the rate-determining step?

The slowest elementary step that limits overall reaction rate Signup and view all the answers

Which of the following statements is true about the rate laws in chemical kinetics?

They express the relationship between the rate and concentration of reactants. Signup and view all the answers

Given the reaction mechanisms, how are elementary steps related to rate laws?

Each elementary step directly corresponds to a rate law. Signup and view all the answers

For the given reaction mechanisms, what role does the concentration of reactants play?

It influences the rate according to the rate laws derived from elementary steps. Signup and view all the answers

What is the role of the rate-determining step in a reaction mechanism?

It is the slowest step that limits the overall reaction rate. Signup and view all the answers

Which statement correctly describes termolecular reactions?

They involve three reactant species at the same time. Signup and view all the answers

In the example provided, what is the observed rate law for the reaction 2NO2 (g) + F2 (g) → 2NO2F (g)?

Rate = k[NO2][F] Signup and view all the answers

What characterizes intermediates in a reaction mechanism?

They are short-lived species not present in the overall reaction. Signup and view all the answers

How is molecularity determined for an elementary step?

By identifying the number of reactant species involved in that specific step. Signup and view all the answers

Which of the following best describes an elementary step in a reaction mechanism?

It represents a single reaction event at the molecular level. Signup and view all the answers

Which of the following statements is true regarding bimolecular reactions?

They involve the collision of two reactant species. Signup and view all the answers

What can be inferred when there are multiple elementary steps leading to a single reaction product?

There may be a rate-determining step among them. Signup and view all the answers

Study Notes

Midterm I

Average score: ~69%
Total points possible: 160 pts
Score achieved: 41.3 pts

Lecture 13: Rate Limiting Steps, Mechanisms, and Catalysis

Topics covered include rate-limiting steps, reaction mechanisms, and catalysis.
Relevant concepts from this lecture include activation energy, temperature effects on reaction rates, and the Arrhenius equation.

Arrhenius Equation

k = A exp(-Ea/RT)
k: rate constant
A: frequency factor
Ea: activation energy
R: ideal gas constant
T: absolute temperature

Two-Point Arrhenius Equation

ln(k₂/k₁) = -Ea/R * (1/T₂ - 1/T₁)

Example: Hydroxylamine Decomposition

Rate constant at 0°C: 0.237 x 10⁻⁴ L mol⁻¹ s⁻¹
Rate constant at 25°C: 2.64 x 10⁻⁴ L mol⁻¹ s⁻¹
Reaction order: 2nd order
Activation energy (Ea): 6.52 x 10⁴ J mol⁻¹
Frequency factor (A): 7.1 x 10⁷ L mol⁻¹ s⁻¹

Reaction Mechanisms from Kinetics

Reactions proceed through a sequence of elementary steps.
Elementary steps define the molecularity of the reaction (unimolecular, bimolecular, termolecular).
Rate laws for each step are identified.
Overall reactions are determined by combining elementary steps.

Rate-Determining Step

The slowest elementary step in a reaction mechanism is the rate-determining step.
The observed rate law corresponds to this step.

Examples of Reaction Mechanisms and Rate-Determining Steps

Specific examples of multi-step reactions involving gas-phase and aqueous-phase reactions are provided.
Reaction intermediates are identified in each process.
Rate-laws for individual steps are noted.

Multi-steps Involving an Equilibrium

Reactions can proceed via series of steps involving reversible steps.
Equilibrium constants and rate constants are linked.

Examples of Reaction Mechanisms

Detailed mechanisms are provided for particular reactions such as the reaction of I−(aq) and OCl−(aq), decomposition of hydroxylamine, and the reaction of NO2 and F2.

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Description

This quiz covers key concepts from Chemistry Lecture 13, focusing on rate-limiting steps, catalytic mechanisms, and the Arrhenius equation. You'll explore topics such as activation energy and the temperature effects on reaction rates, along with practical examples like hydroxylamine decomposition.