Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

6. Thermodynamics and Kinetics

Energy Diagram

Organic Chemistry

6. Thermodynamics and Kinetics

Energy Diagram

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3:07 minutes

Problem 37

Textbook Question

Draw a reaction-energy diagram for a two-step endothermic reaction with a rate-limiting second step.

Verified step by step guidance

Start by understanding the key features of the reaction-energy diagram: the y-axis represents the energy of the system, and the x-axis represents the reaction progress. Since the reaction is endothermic, the energy of the products will be higher than the energy of the reactants.

Identify that the reaction occurs in two steps. Each step will have its own energy barrier (activation energy) and transition state. The second step is rate-limiting, meaning it has the higher activation energy compared to the first step.

Draw the energy of the reactants as a horizontal line on the left side of the diagram. Then, sketch the energy profile for the first step, showing a small peak (transition state) followed by an intermediate that is lower in energy than the peak but higher than the reactants.

For the second step, draw a larger peak (higher activation energy) starting from the intermediate. This peak represents the transition state of the rate-limiting step. The energy of the products should be higher than the energy of the reactants, reflecting the endothermic nature of the reaction.

Label all key points on the diagram: the reactants, the intermediate, the products, the two transition states, and the activation energies for each step. Clearly indicate that the second step has the higher activation energy, making it the rate-limiting step.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reaction Energy Diagram

A reaction energy diagram visually represents the energy changes during a chemical reaction. It typically plots the energy of the reactants, products, and transition states against the reaction coordinate. The diagram helps illustrate the energy barriers that must be overcome for the reaction to proceed, highlighting the differences in energy between the reactants and products.

Endothermic Reaction

An endothermic reaction is a type of chemical reaction that absorbs energy from its surroundings, usually in the form of heat. This results in a net increase in the energy of the products compared to the reactants. In a reaction-energy diagram, endothermic reactions are characterized by a higher energy level of the products relative to the reactants, indicating that energy input is required for the reaction to occur.

Rate-Limiting Step

The rate-limiting step in a multi-step reaction is the slowest step that determines the overall rate of the reaction. It acts as a bottleneck, meaning that even if other steps are faster, the rate of the entire reaction cannot exceed that of the rate-limiting step. In a two-step endothermic reaction, the second step being rate-limiting implies that it has the highest activation energy, which is reflected in the energy diagram as a significant peak.

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Related Practice

Textbook Question

The bromination of methane proceeds through the following steps:

a. Draw a complete reaction-energy diagram for this reaction.

b. Label the rate-limiting step.

Textbook Question

Draw the reaction-energy diagram for the following reverse reaction:

•CH₃ + HCl → CH₄ + Cl•

Textbook Question

Draw a reaction-energy diagram for the following reaction:

•CH₃ + Cl₂ → CH₃Cl + Cl•

The activation energy is 4 kJ/mol (1 kcal/mol), and the overall ΔH° for the reaction is –110 kJ/mol (–27 kcal/mol).

Textbook Question

•CH₃ + Cl₂ → CH₃Cl + Cl•

The activation energy is 4 kJ/mol (1 kcal/mol), and the overall ΔH° for the reaction is –110 kJ/mol (–27 kcal/mol).

b. Give the equation for the reverse reaction.

c. What is the activation energy for the reverse reaction?

Textbook Question

a. Draw an approximate reaction-energy diagram for the acid–base reaction of phenol (see below) with 1-molar aqueous sodium hydroxide solution.

b. On the same diagram, draw an approximate reaction-energy diagram for the acid–base reaction of tert-butyl alcohol (see below) with 1-molar aqueous sodium hydroxide solution.

Textbook Question

Given the reaction coordinate diagram for the reaction of A to form G, answer the following questions:

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a. How many intermediates are formed in the reaction?

b. Which letters represent transition states?

c. What is the fastest step in the reaction?

d. Which is more stable: A or G?

e. Does A or E form faster from C?

f. Which is the more stable intermediate?

Textbook Question

Draw a reaction coordinate diagram for the following reaction in which C is the most stable and B the least stable of the three species and the transition state going from A to B is more stable than the transition state going from B to C:

a. How many intermediates are there?

b. How many transition states are there?

c. Which step has the greater rate constant in the forward direction?

d. Which step has the greater rate constant in the reverse direction?

Textbook Question

a. Which step in the reaction coordinate diagram shown here has the greatest free energy of activation in the forward direction?

b. Is the first-formed intermediate more apt to revert to reactants or go on to form products?

c. Which step is the rate-determining step of the reaction?

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