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

Gibbs Free Energy

Organic Chemistry

6. Thermodynamics and Kinetics

Gibbs Free Energy

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4:40 minutes

Problem 13a

Textbook Question

A certain process has ∆H° = 11.7 kcal/mol and AS° = +33cal/mol•K . That is, this reaction has an unfavorable enthalpy but a favorable entropy term. At what temperature will the process be neither favored nor disfavored?

Verified step by step guidance

Identify the condition for a process to be neither favored nor disfavored. This occurs when the Gibbs free energy change (∆G°) is equal to zero. The equation for Gibbs free energy is:

∆G° = ∆H° - T∆S°

Set ∆G° to zero in the equation:

0 = ∆H° - T∆S°

. Rearrange the equation to solve for temperature (T):

T = ∆H° / ∆S°

Convert the units of ∆H° and ∆S° to ensure consistency. ∆H° is given in kcal/mol, so convert it to cal/mol:

∆H° = 11.7 \, 	ext{kcal/mol} \, × \, 1000 \, 	ext{cal/kcal} = 11700 \, 	ext{cal/mol}

. ∆S° is already in cal/mol·K, so no conversion is needed.

Substitute the values of ∆H° and ∆S° into the equation for T:

T = 11700 \, 	ext{cal/mol} / 33 \, 	ext{cal/mol·K}

Perform the division to calculate the temperature (T) in Kelvin. This will give the temperature at which the process is neither favored nor disfavored.

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Key Concepts

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

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the favorability of a reaction at constant temperature and pressure. It is defined by the equation G = ∆H - T∆S, where ∆H is the change in enthalpy, T is the temperature in Kelvin, and ∆S is the change in entropy. A reaction is spontaneous when G is negative, indicating that the process can occur without external energy input.

Enthalpy (∆H)

Enthalpy (∆H) is a measure of the total heat content of a system. In the context of a chemical reaction, a positive ∆H indicates that the reaction absorbs heat from the surroundings, making it endothermic. This can lead to an unfavorable reaction under certain conditions, as it requires energy input to proceed.

Entropy (∆S)

Entropy (∆S) is a measure of the disorder or randomness in a system. A positive change in entropy suggests that the products of a reaction are more disordered than the reactants, which is generally favorable for spontaneity. In the Gibbs Free Energy equation, a favorable entropy can offset an unfavorable enthalpy, influencing the overall spontaneity of the reaction at different temperatures.

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Related Practice

Textbook Question

a. For a reaction with ∆H° = -12 kcal/mol and ∆S° = 0.01 kcal mol^-1 K^-1, calculate the ∆G° and the equilibrium constant at:

1. 30 °C and 2. 150 °C.

b. How does ∆G° change as T increases?

c. How does K_eq change as T increases?

Textbook Question

(b) Mechanistically, the reaction occurs as shown below. Why is this reaction favored? Based on the stability of the anions, estimate K_eq.

Textbook Question

For the following equilibrium processes and the corresponding ∆G°, indicate whether you expect the equilibrium constant to be greater than, equal to, or less than 1. Justify your expectation in words.

(a)

Textbook Question

For the following values of ∆H° , ∆S°, and T, tell whether the process would be favored.

Textbook Question

Calculate ∆G°, ∆H°, and ∆S° for the following acid–base reactions. Rationalize the value of ∆H° based on the structure of the conjugate bases. [Assume T = 298 K.]

(a)

Textbook Question

Calculate ∆G°, ∆H°, and ∆S° for the following acid–base reactions. Rationalize the value of ∆H° based on the structure of the conjugate bases. [Assume T = 298 K.]

(c)

Textbook Question

Write the rate law for the following reaction and identify which molecules are present in the rate-determining step. Draw a possible transition state and propose a mechanism.

Textbook Question

Third-order reactions are rare. Why do you think that is?

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