Skip to main content
Pearson+ LogoPearson+ Logo
Ch.19 - Chemical Thermodynamics
All textbooksBrown 15th EditionCh.19 - Chemical ThermodynamicsProblem 84a
Chapter 19, Problem 84a

The Kb for methylamine (CH3NH2) at 25 °C is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to Kb.

Verified step by step guidance
1
Identify the base in the problem: Methylamine (CH_3NH_2) is a weak base.
Recall that the base dissociation constant, K_b, is related to the equilibrium of a base reacting with water.
Write the chemical equation for the reaction of methylamine with water: CH_3NH_2 + H_2O \rightleftharpoons CH_3NH_3^+ + OH^-.
Recognize that in this equilibrium, methylamine accepts a proton from water, forming the methylammonium ion (CH_3NH_3^+) and hydroxide ion (OH^-).
Ensure the equation is balanced and represents the equilibrium process for which K_b is defined.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2m
Was this helpful?

Key Concepts

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

Equilibrium Constant (K_b)

The base dissociation constant, K_b, quantifies the strength of a base in solution. It is defined as the ratio of the concentration of the products to the concentration of the reactants at equilibrium for the reaction of a base with water. A higher K_b value indicates a stronger base, as it suggests a greater tendency to accept protons.
Recommended video:
Guided course
01:14
Equilibrium Constant K

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the context of a base like methylamine, this means that the formation of hydroxide ions and the conjugate acid reaches a stable state where their concentrations no longer change over time.
Recommended video:
Guided course
04:21
Chemical Equilibrium Concepts

Methylamine as a Base

Methylamine (CH₃NH₂) is an organic compound that acts as a weak base in aqueous solution. When dissolved in water, it can accept a proton (H⁺) from water, leading to the formation of its conjugate acid (methylammonium ion, CH₃NH₃⁺) and hydroxide ions (OH⁻). This reaction is essential for writing the equilibrium expression for K_b.
Recommended video:
Guided course
01:17
Base Example
Related Practice
Textbook Question

The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (b) By using the value of Ka, calculate ΔG° for the dissociation of nitrous acid in aqueous solution.

Textbook Question

The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (c) What is the value of ΔG at equilibrium?

Textbook Question

The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (d) What is the value of ΔG when [H+] = 5.0⨉10-2 M, [NO2-] = 6.0⨉10-4 M, and [HNO2] = 0.20 M?

Textbook Question

The Kb for methylamine (CH3NH2) at 25 °C is given in Appendix D. (d) What is the value of ΔG when [H+] = 6.7 × 10-9 M, [CH3NH3+] = 2.4 × 10-3 M, and [CH3NH2] = 0.098 M?

Textbook Question

(a) Which of the thermodynamic quantities T, E, q, w, and S are state functions? (b) Which depend on the path taken from one state to another?

1
views
Textbook Question

(d) For a reversible isothermal process, write an expression for ΔE in terms of q and w and an expression for ΔS in terms of q and T.