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Ch.20 - Electrochemistry
Brown - Chemistry: The Central Science 15th Edition
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Tutti i libri di testoBrown 15th EditionCh.20 - ElectrochemistryProblema 55b
Capitolo 20, Problema 55b

Given the following reduction half-reactions:
Fe3+(aq) + e- → Fe2+(aq) E°red = +0.77 V
S2O62-(aq) + 4 H+(aq) + 2 e- → 2 H2SO3(aq) E°red = +0.60 V
N2O(g) + 2 H+(aq) + 2 e- → N2(g) + H2O(l) E°red = -1.77 V
VO2+(aq) + 2 H+(aq) + e- → VO2+ + H2O(l) E°red = +1.00 V
(b) Calculate ∆G° for each reaction at 298 K.

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Identify the formula to calculate the standard Gibbs free energy change (\( \Delta G^\circ \)) for a redox reaction: \( \Delta G^\circ = -nFE^\circ_{cell} \), where \( n \) is the number of moles of electrons transferred, \( F \) is the Faraday constant (approximately 96485 C/mol), and \( E^\circ_{cell} \) is the standard cell potential.
For each half-reaction, determine the number of electrons transferred (\( n \)) from the balanced equation.
Calculate the standard cell potential (\( E^\circ_{cell} \)) for each reaction. Since these are reduction half-reactions, \( E^\circ_{cell} \) is simply the given \( E^\circ_{red} \) value for each reaction.
Substitute the values of \( n \), \( F \), and \( E^\circ_{cell} \) into the \( \Delta G^\circ \) formula for each reaction to find the standard Gibbs free energy change.
Ensure the units are consistent, typically converting \( \Delta G^\circ \) to kJ/mol by dividing the result by 1000, as \( F \) is in C/mol and \( E^\circ_{cell} \) is in V (J/C).

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Standard Reduction Potential (E°red)

Standard reduction potential (E°red) is a measure of the tendency of a chemical species to gain electrons and be reduced. It is measured in volts and is determined under standard conditions (1 M concentration, 1 atm pressure, and 25°C). A higher E°red value indicates a greater likelihood of reduction occurring, which is crucial for predicting the direction of redox reactions.
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Standard Reduction Potentials

Gibbs Free Energy (∆G°)

Gibbs free energy (∆G°) is a thermodynamic quantity that indicates the spontaneity of a reaction at constant temperature and pressure. It is calculated using the equation ∆G° = -nFE°cell, where n is the number of moles of electrons transferred, F is Faraday's constant, and E°cell is the cell potential. A negative ∆G° value signifies that the reaction is spontaneous under standard conditions.
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Gibbs Free Energy of Reactions

Half-Reaction Method

The half-reaction method involves breaking down redox reactions into their oxidation and reduction components. Each half-reaction can be analyzed separately to determine the E°red values and the overall cell potential. This method is essential for calculating the Gibbs free energy change for the entire reaction, as it allows for the identification of the number of electrons transferred and the respective potentials involved.
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Method 1 of Radioactive Half-Life
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Domanda del libro di testo

For each of the following reactions, write a balanced equation, calculate the standard emf, calculate ∆G° at 298 K, and calculate the equilibrium constant K at 298 K. (b) In acidic solution, copper(I) ion is oxidized to copper(II) ion by nitrate ion.

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Domanda del libro di testo

For each of the following reactions, write a balanced equation, calculate the standard emf, calculate ∆G° at 298 K, and calculate the equilibrium constant K at 298 K. (a) Aqueous iodide ion is oxidized to I21s2 by Hg22+1aq2.

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Domanda del libro di testo

Given the following reduction half-reactions:

Fe3+(aq) + e- → Fe2+(aq) E°red = +0.77 V

S2O62-(aq) + 4 H+(aq) + 2 e- → 2 H2SO3(aq) E°red = +0.60 V

N2O(g) + 2 H+(aq) + 2 e- → N2(g) + H2O(l) E°red = -1.77 V

VO2+(aq) + 2 H+(aq) + e- → VO2+ + H2O(l) E°red = +1.00 V

(a) Write balanced chemical equations for the oxidation of Fe2+(aq) by S2O62-(aq), by N2O(aq), and by VO2+(aq).

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Domanda del libro di testo

Given the following reduction half-reactions:

Fe3+(aq) + e- → Fe2+(aq) E°red = +0.77 V

S2O62-(aq) + 4 H+(aq) + 2 e- → 2 H2SO3(aq) E°red = +0.60 V

N2O(g) + 2 H+(aq) + 2 e- → N2(g) + H2O(l) E°red = -1.77 V

VO2+(aq) + 2 H+(aq) + e- → VO2+ + H2O(l) E°red = +1.00 V

(c) Calculate the equilibrium constant K for each reaction at 298 K.

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