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 38d

Textbook Question

Calculate K_eq for these acid–base reactions.
(d)

Verified step by step guidance

Step 1: Identify the acid and base on both sides of the reaction. In this case, the alcohol (CH3CH2OH) acts as the acid, and hydroxide ion (OH⁻) acts as the base. On the product side, the ethoxide ion (CH3CH2O⁻) is the conjugate base, and water (H2O) is the conjugate acid.

Step 2: Determine the pKa values of the acid and conjugate acid. The pKa of ethanol (CH3CH2OH) is approximately 16, and the pKa of water (H2O) is approximately 15.7.

Step 3: Use the relationship between pKa values and equilibrium constant (Keq). The formula is: Keq = 10^(pKa(conjugate acid) - pKa(acid)).

Step 4: Substitute the pKa values into the formula. Here, pKa(conjugate acid) = 15.7 (for H2O) and pKa(acid) = 16 (for CH3CH2OH).

Step 5: Calculate the exponent (pKa difference) and express the equilibrium constant (Keq) in terms of 10 raised to the power of the difference. This will give the final Keq value for the reaction.

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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, quantifies the ratio of the concentrations of products to reactants at equilibrium for a given reaction. It is calculated using the formula K_eq = [products]/[reactants], where the concentrations are raised to the power of their coefficients in the balanced equation. A K_eq greater than 1 indicates that products are favored, while a value less than 1 suggests that reactants are favored.

Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between reactants. In these reactions, acids donate protons, while bases accept them. Understanding the strength of acids and bases, often represented by their dissociation constants (K_a for acids and K_b for bases), is crucial for predicting the direction of the reaction and calculating K_eq.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed, the system will adjust to counteract the disturbance and restore a new equilibrium. This principle is essential in predicting how changes in concentration, pressure, or temperature will affect the position of equilibrium in acid-base reactions, thereby influencing the calculation of K_eq.

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Related Practice

Textbook Question

Calculate the equilibrium constant for each of the acid–base reactions shown.

Textbook Question

Predict the K_eq for the following acid–base reaction.

Textbook Question

We usually calculate K_eq for acid–base reactions using pK_a values.

(a) Derive an equation to calculate K_eq using pK_b values, then

(b) use it to calculate the equilibrium constant for the following reaction.

Textbook Question

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

(b)

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

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

(c)

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.

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Calculate Keq for these acid–base reactions.(d)

Key Concepts

Equilibrium Constant (K_eq)

Acid-Base Reactions

Le Chatelier's Principle

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Calculate K_eq for these acid–base reactions.
(d)