Ch.19 - Electrochemistry

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McMurry 8th Edition

Ch.19 - Electrochemistry

Problema 103

Capitolo 19, Problema 103

At one time on Earth, iron was present mostly as iron(II). Later, once plants had produced a significant quantity of oxygen in the atmosphere, the iron became oxidized to iron(III). Show that Fe2+(aq) can be spontaneously oxidized to Fe3+(aq) by O2(g) at 25°C assuming the following reasonable environmental conditions:

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Identify the half-reactions involved in the oxidation of Fe^{2+} to Fe^{3+} and the reduction of O_2 to H_2O.

Write the oxidation half-reaction: Fe^{2+} \(\rightarrow\) Fe^{3+} + e^{-}.

Write the reduction half-reaction: O_2 + 4H^+ + 4e^{-} \(\rightarrow\) 2H_2O.

Determine the standard reduction potentials (E^\(\circ\)) for both half-reactions from a standard reduction potential table.

Calculate the standard cell potential (E^\(\circ\)_{cell}) using the formula: E^\(\circ\)_{cell} = E^\(\circ\)_{cathode} - E^\(\circ\)_{anode}. If E^\(\circ\)_{cell} is positive, the reaction is spontaneous.

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Oxidation and Reduction

Oxidation refers to the loss of electrons from a substance, while reduction is the gain of electrons. In the context of the question, Fe2+ is oxidized to Fe3+ as it loses an electron, and O2 acts as the oxidizing agent, facilitating this process. Understanding these concepts is crucial for analyzing redox reactions.

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01:53

Oxidation and Reduction Reactions

Standard Electrode Potentials

Standard electrode potentials (E°) provide a measure of the tendency of a chemical species to be reduced. The difference in E° values between the half-reactions of Fe2+/Fe3+ and O2/H2O can be used to determine the spontaneity of the reaction. A positive cell potential indicates that the reaction can occur spontaneously under standard conditions.

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01:27

Standard Cell Potential

Gibbs Free Energy

Gibbs free energy (ΔG) is a thermodynamic potential that helps predict the spontaneity of a reaction. A negative ΔG indicates that a reaction can occur spontaneously. The relationship between ΔG, the standard electrode potential, and temperature is essential for determining whether the oxidation of Fe2+ by O2 is thermodynamically favorable.

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01:51

Gibbs Free Energy of Reactions

Pratica correlata

Domanda del libro di testo

What is the pH of the solution in the cathode compartment of the following cell if the measured cell potential at 25 °C is 0.17 V?

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Domanda del libro di testo

Copper reduces dilute nitric acid to nitric oxide (NO) but reduces concentrated nitric acid to nitrogen dioxide (NO2): Assuming that [Cu2+] = 0.10 M and that the partial pressures of NO and NO2 are 1.0 * 10-3 atm, calculate the potential (E) for reactions (1) and (2) at 25 °C and show which reaction has the greater thermodynamic tendency to occur when the concentration of HNO3 is (a) 1.0 M

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Domanda del libro di testo

When suspected drunk drivers are tested with a Breathalyzer, the alcohol (ethanol) in the exhaled breath is oxidized to acetic acid with an acidic solution of potassium dichromate: The color of the solution changes because some of the orange Cr₂O₇^2-is converted to the green Cr³⁺ The Breathalyzer measures the color change and produces a meter reading calibrated in blood alcohol content. (a) What is E° for the reaction if the standard half-cell potential for the reduction of acetic acid to ethanol is 0.058 V?

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Domanda del libro di testo

When suspected drunk drivers are tested with a Breathalyzer, the alcohol (ethanol) in the exhaled breath is oxidized to acetic acid with an acidic solution of potassium dichromate: The color of the solution changes because some of the orange Cr₂O₇^2-is converted to the green Cr³⁺ The Breathalyzer measures the color change and produces a meter reading calibrated in blood alcohol content. (b) What is the value of E for the reaction when the concentrations of ethanol, acetic acid, Cr₂O₇ are 1.0 M and the pH is 4.00?

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