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

Entropy

Organic Chemistry

6. Thermodynamics and Kinetics

Entropy

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4:09 minutes

Problem 21

Textbook Question

a. For which reaction in each set will ∆S° be more significant?
b. For which reaction will ∆S° be positive?
1. A ⇌ B or A + B ⇌ C
2. A ⇌ B + C or A + B ⇌ C + D

Verified step by step guidance

Step 1: Understand the concept of entropy (∆S°). Entropy is a measure of the disorder or randomness in a system. A positive ∆S° indicates an increase in disorder, while a negative ∆S° indicates a decrease in disorder.

Step 2: Analyze the first set of reactions: A → B versus A + B → C. In the first reaction, a single molecule (A) is converted into another single molecule (B), so there is no significant change in the number of particles or disorder. In the second reaction, two molecules (A and B) combine to form one molecule (C), which decreases the number of particles and reduces disorder. Therefore, the first reaction will have a more significant ∆S°.

Step 3: Determine which reaction in the first set will have a positive ∆S°. Since the first reaction (A → B) does not involve a change in the number of particles, ∆S° is likely to be close to zero or slightly positive. The second reaction (A + B → C) involves a decrease in the number of particles, so ∆S° will be negative. Thus, the first reaction is more likely to have a positive ∆S°.

Step 4: Analyze the second set of reactions: A → B + C versus A + B → C + D. In the first reaction, one molecule (A) breaks into two molecules (B and C), increasing the number of particles and disorder. In the second reaction, two molecules (A and B) combine to form two molecules (C and D), so the number of particles remains constant, and there is no significant change in disorder. Therefore, the first reaction will have a more significant ∆S°.

Step 5: Determine which reaction in the second set will have a positive ∆S°. In the first reaction (A → B + C), the number of particles increases, leading to an increase in disorder and a positive ∆S°. In the second reaction (A + B → C + D), the number of particles remains constant, so ∆S° is likely to be close to zero. Thus, the first reaction is more likely to have a positive ∆S°.

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Key Concepts

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

Entropy (∆S°)

Entropy, denoted as ∆S°, is a measure of the disorder or randomness in a system. In chemical reactions, a positive change in entropy indicates an increase in disorder, often associated with the formation of more molecules or the breaking of bonds. Understanding how to evaluate changes in entropy is crucial for predicting the spontaneity of reactions.

Reaction Types

The two types of reactions presented are equilibrium reactions (A <--> B) and combination reactions (A + B <--> C). Equilibrium reactions involve the conversion of reactants to products and vice versa, while combination reactions involve the formation of a single product from multiple reactants. Recognizing these types helps in analyzing how entropy changes in each scenario.

Significance of ∆S° in Reactions

The significance of ∆S° in a reaction can be assessed by considering the number of molecules involved. Generally, reactions that produce more gas molecules or involve the dissociation of a compound tend to have a greater positive ∆S°. This concept is essential for determining which reaction will have a more significant entropy change and whether that change will be positive.

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Related Practice

Textbook Question

For each reaction, estimate whether ΔS° for the reaction is positive, negative, or impossible to predict.

(a)

Textbook Question

When ethene is mixed with hydrogen in the presence of a platinum catalyst, hydrogen adds across the double bond to form ethane. At room temperature, the reaction goes to completion. Predict the signs of ΔH° and ΔS° for this reaction. Explain these signs in terms of bonding and freedom of motion.

Textbook Question

For each reaction, estimate whether ΔS° for the reaction is positive, negative, or impossible to predict.

(b)

Textbook Question

For each reaction, estimate whether ΔS° for the reaction is positive, negative, or impossible to predict.

(c)

Textbook Question

a. Which of the following reactions has the larger ∆S° value?

b. Is the ∆S° value positive or negative?

Textbook Question

At what temperature does the entropy change of a process not contribute to the favorability of a process?

Textbook Question

The hydrogenation of alkenes is a reaction we study in Chapter 9.

(b) Is this reaction favored or disfavored in terms of entropy?

Textbook Question

Through the course of this chapter, we have discussed only alkane chlorination and bromination, yet there are two other halogens we have not discussed.

(b) Is radical iodination a favorable reaction? Do you expect it to be selective? Show your calculations.

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a. For which reaction in each set will ∆S° be more significant?b. For which reaction will ∆S° be positive?1. A ⇌ B or A + B ⇌ C2. A ⇌ B + C or A + B ⇌ C + D

Key Concepts

Entropy (∆S°)

Reaction Types

Significance of ∆S° in Reactions

Watch next

a. For which reaction in each set will ∆S° be more significant?
b. For which reaction will ∆S° be positive?
1. A ⇌ B or A + B ⇌ C
2. A ⇌ B + C or A + B ⇌ C + D