Ch.20 - Electrochemistry

Brown - Chemistry: The Central Science 15th Edition

Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970당신이 사용하는 게 아니라요?교과서 변경

Brown 15th Edition

Ch.20 - Electrochemistry

문제 104b,c

20장, 문제 104b,c

A voltaic cell is constructed that uses the following half-cell reactions:
Cu⁺(aq) + e^- → Cu(s)
I₂(s) + 2 e^- → 2 I^-(aq)
The cell is operated at 298 K with [Cu⁺] = 0.25 M and [I^-] = 0.035 M.
(b) Which electrode is the anode of the cell?
(c) Is the answer to part (b) the same as it would be if the cell were operated under standard conditions?

검증된 단계별 안내

Identify the oxidation and reduction half-reactions. In the given cell, Cu+(aq) + e- → Cu(s) is the reduction half-reaction, and I2(s) + 2 e- → 2 I-(aq) is the oxidation half-reaction.

Determine which electrode is the anode. The anode is where oxidation occurs. Since I2 is being reduced to I-, the I2/I- half-cell is the anode.

Consider the standard cell potential (E°) for each half-reaction. Under standard conditions, the half-reaction with the lower (more negative) standard reduction potential is the anode.

Compare the cell operation under non-standard conditions to standard conditions. Under non-standard conditions, the concentrations of the ions can affect the cell potential, but the identity of the anode and cathode is determined by the direction of electron flow.

Conclude whether the anode remains the same under standard conditions. Since the identity of the anode is based on the inherent tendency of the half-reactions to oxidize or reduce, it should remain the same under standard conditions.

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주요 개념

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Voltaic Cell and Electrode Reactions

A voltaic cell generates electrical energy through spontaneous redox reactions. In this setup, oxidation occurs at the anode, where electrons are released, while reduction occurs at the cathode, where electrons are accepted. Understanding the half-cell reactions is crucial to identify which species is oxidized and which is reduced, thus determining the anode and cathode.

Standard Conditions and Nernst Equation

Standard conditions refer to a set of specific conditions (1 M concentration, 1 atm pressure, and 25°C) under which the standard electrode potentials are measured. The Nernst equation relates the cell potential to the concentrations of the reactants and products, allowing for the calculation of cell potential under non-standard conditions. This is essential for comparing the behavior of the cell under varying concentrations.

Electrode Designation: Anode vs. Cathode

In electrochemistry, the anode is defined as the electrode where oxidation occurs, while the cathode is where reduction takes place. The designation of electrodes can change based on the direction of electron flow and the specific reactions involved. Understanding how to identify these electrodes based on the half-reactions is key to answering questions about the cell's operation and behavior under different conditions.

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교과서 질문

The capacity of batteries such as the typical AA alkaline battery is expressed in units of milliamp-hours (mAh). An AA alkaline battery yields a nominal capacity of 2850 mAh. (b) The starting voltage of a fresh alkaline battery is 1.55 V. The voltage decreases during discharge and is 0.80 V when the battery has delivered its rated capacity. If we assume that the voltage declines linearly as current is withdrawn, estimate the total maximum electrical work the battery could perform during discharge.

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교과서 질문

A voltaic cell is constructed that uses the following half-cell reactions:

Cu⁺(aq) + e^- → Cu(s)

I₂(s) + 2 e^- → 2 I^-(aq)

The cell is operated at 298 K with [Cu⁺] = 0.25 M and [I^-] = 0.035 M.

(a) Determine E for the cell at these concentrations.

Disulfides are compounds that have S ¬ S bonds, like peroxides have O ¬ O bonds. Thiols are organic compounds that have the general formula R ¬ SH, where R is a generic hydrocarbon. The SH- ion is the sulfur counterpart of hydroxide, OH-. Two thiols can react to make a disulfide, R ¬ S ¬ S ¬ R. (b) What is the oxidation state of sulfur in a disulfide?

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교과서 질문

Disulfides are compounds that have S ¬ S bonds, like peroxides have O ¬ O bonds. Thiols are organic compounds that have the general formula R ¬ SH, where R is a generic hydrocarbon. The SH- ion is the sulfur counterpart of hydroxide, OH-. Two thiols can react to make a disulfide, R ¬ S ¬ S ¬ R. (c) If you react two thiols to make a disulfide, are you oxidizing or reducing the thiols?

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