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 2

Textbook Question

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

Verified step by step guidance

Identify the chemical reaction between ethylamine (C2H5NH2) and propanoic acid (C2H5COOH). The reaction is a typical acid-base reaction where ethylamine acts as a base and propanoic acid acts as an acid.

Write the balanced chemical equation for the reaction: C2H5NH2 + C2H5COOH ⇌ C2H5NH3+ + C2H5COO−.

Determine the expression for the equilibrium constant (K_eq) for the reaction. The equilibrium constant expression is given by: K_eq = ([C2H5NH3+][C2H5COO−]) / ([C2H5NH2][C2H5COOH]).

Use the known pKa values of the acid (propanoic acid) and the conjugate acid (ethylammonium ion) to calculate the equilibrium constant. The relationship between pKa and K_eq can be used: K_eq = 10^(pKa(base) - pKa(acid)).

Analyze the calculated K_eq value to determine which side of the reaction is favored. If K_eq > 1, the products are favored; if K_eq < 1, the reactants are favored.

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Key Concepts

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

Equilibrium Constant (K)

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

Acid-Base Reaction

An acid-base reaction involves the transfer of protons (H+) between an acid and a base. In this context, propanoic acid acts as the acid, donating a proton, while ethylamine acts as the base, accepting the proton. Understanding the strength of the acid and base involved is crucial, as stronger acids and bases will influence the position of equilibrium and the value of the equilibrium constant.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed by a change in concentration, temperature, or pressure, the system will adjust to counteract the disturbance and restore a new equilibrium. This principle helps predict how changes in conditions will affect the position of equilibrium, allowing us to determine which side of the reaction is favored based on the equilibrium constant and the nature of the reactants and products.

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Related Practice

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.

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)

Textbook Question

Given that the indicated pK_a values correspond to the acid dissociation reactions shown, calculate the ratio of acid to conjugate base for the reactions shown.

(a)

Textbook Question

Using pK_a values, calculate an approximate K_eq value for the following substitution reaction.

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