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Ch.19 - Chemical Thermodynamics
All textbooksBrown 15th EditionCh.19 - Chemical ThermodynamicsProblem 83c
Chapter 19, Problem 83c

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?

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insert step 1> Identify the relationship between the equilibrium constant (K) and the Gibbs free energy change (ΔG) at equilibrium. The equation is ΔG = -RT ln(K), where R is the universal gas constant and T is the temperature in Kelvin.
insert step 2> Convert the temperature from Celsius to Kelvin by adding 273.15 to the given temperature in Celsius.
insert step 3> Use the value of the gas constant R, which is 8.314 J/(mol·K).
insert step 4> Look up the value of the equilibrium constant K for nitrous acid (HNO2) from Appendix D.
insert step 5> Substitute the values of R, T, and K into the equation ΔG = -RT ln(K) to find the Gibbs free energy change at equilibrium.

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Key Concepts

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

Acid Dissociation Constant (K<sub>a</sub>)

The acid dissociation constant (K<sub>a</sub>) quantifies the strength of an acid in solution. It is defined as the equilibrium constant for the dissociation of an acid into its conjugate base and a proton. A higher K<sub>a</sub> value indicates a stronger acid, meaning it dissociates more completely in solution. Understanding K<sub>a</sub> is essential for predicting the behavior of acids in chemical reactions.
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Equilibrium Constant K

Gibbs Free Energy (ΔG)

Gibbs free energy (ΔG) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. At equilibrium, ΔG is zero, indicating that the system is in a state of balance and no net change occurs. The relationship between ΔG and K<sub>a</sub> can be expressed by the equation ΔG = -RT ln(K<sub>a</sub>), linking thermodynamics and chemical equilibrium.
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Gibbs Free Energy of Reactions

Equilibrium in Chemical Reactions

Equilibrium in chemical reactions refers to the state where the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. At this point, the system has reached a dynamic balance, and the concentrations do not change over time. Understanding equilibrium is crucial for calculating ΔG and interpreting the behavior of acids and bases in solution.
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Chemical Equilibrium Concepts
Related Practice
Textbook Question

Consider the reaction PbCO3(s) ⇌ PbO(s) + CO2(g) Using data in Appendix C, calculate the equilibrium pressure of CO2 in the system at (a) 400 °C (b) 180 °C.

Textbook Question

The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to Ka.

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. (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. (a) Write the chemical equation for the equilibrium that corresponds to Kb.

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?