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

3. Acids and Bases

Equilibrium Constant

Organic Chemistry

3. Acids and Bases

Equilibrium Constant

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Problem 21c

Textbook Question

Write the K_eq expression for the following acid–base reactions. [You don't need to calculate K_eq here.]
(c)

Verified step by step guidance

Step 1: Identify the acid and base on the reactant side. In this reaction, cyclopentanethiol (SH group) acts as the acid, and isopropoxide (-O group) acts as the base.

Step 2: Identify the conjugate acid and conjugate base on the product side. Cyclopentanethiolate (S⁻ group) is the conjugate base, and isopropanol (HO group) is the conjugate acid.

Step 3: Write the equilibrium constant expression (Keq) for the acid-base reaction. Keq is defined as the ratio of the concentrations of the products to the concentrations of the reactants.

Step 4: Use the chemical species to construct the Keq expression. The general form is: Keq = [Products]/[Reactants]. For this reaction, Keq = ([Cyclopentanethiolate] × [Isopropanol]) / ([Cyclopentanethiol] × [Isopropoxide]).

Step 5: Ensure that the expression includes only the species involved in the equilibrium and that it reflects the stoichiometry of the reaction. Double-check that the charges and chemical formulas are correctly represented.

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Key Concepts

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

Equilibrium Constant (K_eq)

The equilibrium constant (K_eq) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given chemical reaction. It is derived from the law of mass action and is specific to a particular reaction at a given temperature. For acid-base reactions, K_eq can indicate the strength of the acids and bases involved.

Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H⁺ ions) between reactants. In these reactions, acids donate protons while bases accept them. Understanding the nature of the acids and bases involved is crucial for writing the correct K_eq expression, as it determines the direction of the equilibrium and the species present at equilibrium.

Writing K_eq Expressions

To write the K_eq expression for an acid-base reaction, one must identify the products and reactants and express the equilibrium constant as the ratio of the concentrations of the products raised to their stoichiometric coefficients over the concentrations of the reactants raised to their coefficients. This process requires careful attention to the balanced chemical equation and the states of the compounds involved.

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Related Practice

Textbook Question

Given the pK_b, calculate the pK_a of the conjugate acid.

(b)

Textbook Question

Calculate K_eq for these acid–base reactions.

(d)

Textbook Question

Using pK_a values for the conjugate acids of the bases on each side of the reaction arrow, identify which side of the equilibrium would be favored in the following hypothetical reactions.

(c)

Textbook Question

Calculate K_eq for the acid–base reaction shown. Which side is favored and why?

Textbook Question

Parts (a)–(d) of this assessment assist in the development of what will become a common theme in organic reactions and should be worked in order. [Think carefully about how each question relates to the others.]

(c) Without worrying about the mechanism of the reaction, estimate an equilibrium constant for the following carbonyl addition reaction based on the relative stability of the Lewis bases.

Textbook Question

Calculate the equilibrium constant for the reaction of ethylamine and propanoic acid. Which side is favored?

Textbook Question

How do you know that a proton with a low pK_a value is acidic (besides 'I just remember')?

Textbook Question

For the following acid–base pairs, (iv) calculate K_eq;

(e)

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Write the Keq expression for the following acid–base reactions. [You don't need to calculate Keq here.](c)

Key Concepts

Equilibrium Constant (K_eq)

Acid-Base Reactions

Writing K_eq Expressions

Watch next

Write the K_eq expression for the following acid–base reactions. [You don't need to calculate K_eq here.]
(c)