Ch.20 - Electrochemistry

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.20 - Electrochemistry

Problema 81a

Capitolo 20, Problema 81a

A voltaic cell consists of a Zn/Zn²⁺ half-cell and a Ni/Ni²⁺ half-cell at 25 °C. The initial concentrations of Ni²⁺ and Zn²⁺ are 1.50 M and 0.100 M, respectively. a. What is the initial cell potential?

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Identify the half-reactions for the voltaic cell: Zn -> Zn^{2+} + 2e^- and Ni^{2+} + 2e^- -> Ni.

Look up the standard reduction potentials (E°) for each half-reaction: E°(Zn^{2+}/Zn) and E°(Ni^{2+}/Ni).

Calculate the standard cell potential (E°_{cell}) using the formula: E°_{cell} = E°(cathode) - E°(anode).

Use the Nernst equation to calculate the initial cell potential (E_{cell}): E_{cell} = E°_{cell} - (RT/nF) * ln(Q), where Q is the reaction quotient.

Substitute the given concentrations into the reaction quotient Q = [Zn^{2+}]/[Ni^{2+}] and solve for E_{cell} using the Nernst equation.

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Voltaic Cell

A voltaic cell, also known as a galvanic cell, is an electrochemical cell that converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two half-cells, each containing an electrode and an electrolyte. The flow of electrons from the anode to the cathode generates an electric current, and the cell potential is determined by the difference in reduction potentials of the two half-reactions.

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01:21

The Electrolytic Cell

Nernst Equation

The Nernst equation relates the cell potential to the concentrations of the reactants and products in a redox reaction. It is expressed as E = E° - (RT/nF) ln(Q), where E° is the standard cell potential, R is the universal gas constant, T is the temperature in Kelvin, n is the number of moles of electrons transferred, F is Faraday's constant, and Q is the reaction quotient. This equation allows for the calculation of the cell potential under non-standard conditions.

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01:17

The Nernst Equation

Standard Reduction Potentials

Standard reduction potentials are measured voltages that indicate the tendency of a species to gain electrons and be reduced, measured under standard conditions (1 M concentration, 1 atm pressure, and 25 °C). Each half-reaction has a specific standard reduction potential, and the overall cell potential can be calculated by subtracting the anode potential from the cathode potential. These values are crucial for determining the feasibility and strength of electrochemical reactions.

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01:10

Standard Reduction Potentials

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An electrochemical cell is based on these two half-reactions:

Ox: Pb(s) → Pb²⁺(aq, 0.10 M) + 2 e^–

Red: MnO₄^–(aq, 1.50 M) + 4 H⁺(aq, 2.0 M) + 3 e^– → MnO₂(s) + 2 H₂O(l)

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Ox: Sn(s) → Sn²⁺(aq, 2.00 M) + 2 e^–

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A voltaic cell consists of a Zn/Zn²⁺ half-cell and a Ni/Ni²⁺ half-cell at 25 °C. The initial concentrations of Ni²⁺ and Zn²⁺ are 1.50 M and 0.100 M, respectively. c. What are the concentrations of Ni²⁺ and Zn²⁺ when the cell potential falls to 0.45 V?

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A voltaic cell consists of a Zn/Zn²⁺ half-cell and a Ni/Ni²⁺ half-cell at 25 °C. The initial concentrations of Ni²⁺ and Zn²⁺ are 1.50 M and 0.100 M, respectively. b. What is the cell potential when the concentration of Ni²⁺ has fallen to 0.500 M?

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A voltaic cell consists of a Pb/Pb²⁺ half-cell and a Cu/Cu²⁺ half-cell at 25°C. The initial concentrations of Pb²⁺ and Cu²⁺ are 0.0500 M and 1.50 M, respectively. a. What is the initial cell potential?

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A voltaic cell consists of a Zn/Zn2+ half-cell and a Ni/Ni2+ half-cell at 25 °C. The initial concentrations of Ni2+ and Zn2+ are 1.50 M and 0.100 M, respectively. a. What is the initial cell potential?

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Concetti chiave

Voltaic Cell

Nernst Equation

Standard Reduction Potentials

A voltaic cell consists of a Zn/Zn²⁺ half-cell and a Ni/Ni²⁺ half-cell at 25 °C. The initial concentrations of Ni²⁺ and Zn²⁺ are 1.50 M and 0.100 M, respectively. a. What is the initial cell potential?