20. Electrochemistry

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Multiple Choice

Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C.

3 Cl₂ (g) + 2 Fe (s) → 6 Cl^–(aq) + 2 Fe³⁺(aq)

Standard Reduction Potentials

Cl₂(g) + 2 e^– → 2 Cl^–(aq) E°_red = + 1.396 V
Fe³⁺(aq) + 3 e^– → Fe(s) E°_red = – 0.040 V

138

Multiple Choice

Predict whether the following reaction will occur as written based on the calculated E^ºcell.

Ag⁺(aq) + Au (s) → Ag (s) + Au³⁺(aq)

Standard Reduction Potentials

Ag⁺(aq) + e^– → Ag (s) E°_red = + 0.80 V
Au³⁺(aq) + 3 e^– → Au(s) E°_red = + 1.50 V

134

A voltaic cell that uses the reaction PdCl42-1aq2 + Cd1s2 ¡ Pd1s2 + 4 Cl-1aq2 + Cd2+1aq2 has a measured standard cell potential of +1.03 V. (b) By using data from Appendix E, determine E°red for the reaction involving Pd.

354

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions: (c) Fe1s2 + 2 Fe3+1aq2 ¡ 3 Fe2+1aq2

231

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions: (b) Ni1s2 + 2 Ce4+1aq2 ¡ Ni2+1aq2 + 2 Ce3+1aq2

679

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions: (a) Cl21g2 + 2 I-1aq2 ¡ 2 Cl-1aq2 + I21s2

386

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions: (d) 2 NO3-1aq2 + 8 H+1aq2 + 3 Cu1s2 ¡ 2 NO1g2 + 4 H2O1l2 + 3 Cu2+1aq2

769

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The standard reduction potentials of the following halfreactions are given in Appendix E: Ag+1aq2 + e- ¡ Ag1s2 Cu2+1aq2 + 2 e- ¡ Cu1s2 Ni2+1aq2 + 2 e- ¡ Ni1s2 Cr3+1aq2 + 3 e- ¡ Cr1s2 (b) Determine which combination of these half-cell reactions leads to the cell reaction with the smallest positive cell potential and calculate the value.

842

Calculate the standard cell potential for each of the electro- chemical cells in Problem 43.

940

Determine whether or not each redox reaction occurs spontaneously in the forward direction. a. Ni(s) + Zn2+(aq) ¡ Ni2+(aq) + Zn(s)

1289

Determine whether or not each redox reaction occurs spontaneously in the forward direction. b. 2 Ag+(aq) + Ni(s) ¡ 2 Ag(s) + Ni2+(aq)

1426

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written. b. MnO2(aq) + 4 H+(aq) + Zn(s) ¡ Mn2+(aq) + 2H2O(l) + Zn2+(aq)

348

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written. a. 2 Cu(s) + Mn2+(aq) ¡ 2 Cu+(aq) + Mn(s)

1093

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written. c. PbO2(s) + 4 H+(aq) + Sn(s) ¡ Pb2+(aq) + 2H2O(l) + Sn2+(aq)

741

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written. a. O2(g) + 2 H2O(l) + 4 Ag(s) ¡ 4 OH-(aq) + 4 Ag+(aq)

741

A voltaic cell utilizes the following reaction: 4 Fe2+1aq2 + O21g2 + 4 H+1aq2 ¡ 4 Fe3+1aq2 + 2 H2O1l2 (a) What is the emf of this cell under standard conditions?

319

A voltaic cell utilizes the following reaction: 2 Fe3+1aq2 + H21g2 ¡ 2 Fe2+1aq2 + 2 H+1aq2 (a) What is the emf of this cell under standard conditions?

366

Heart pacemakers are often powered by lithium–silver chromate 'button' batteries. The overall cell reaction is 2 Li1s2 + Ag2CrO41s2 ¡ Li2CrO41s2 + 2 Ag1s2 (b) Choose the two half-reactions from Appendix E that most closely approximate the reactions that occur in the battery. What standard emf would be generated by a voltaic cell based on these half-reactions?

725

In some applications nickel–cadmium batteries have been replaced by nickel–zinc batteries. The overall cell reaction for this relatively new battery is: 2 H2O1l2 + 2 NiO1OH21s2 + Zn1s2 ¡ 2 Ni1OH221s2 + Zn1OH221s2 (d) Would you expect the specific energy density of a nickel–zinc battery to be higher or lower than that of a nickel–cadmium battery?

491

The following cell reactions occur spontaneously: (c) Which of the three cell reactions delivers the highest voltage?

230

Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. (d) Reduction of I2(s) by H2SO3(aq)

313

Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. (c) Oxidation of Ag(s) by Pb2+(aq)

253

Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. (b) Reduction of Ni2+(aq) by Sn2+(aq)

223

Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. (a) Oxidation of Sn2+(aq) by Br2(aq)

435

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(a) Which reaction is spontaneous in the hydrogen fuel cell: hydrogen gas plus oxygen gas makes water, or water makes hydrogen gas plus oxygen gas?

773

Refer to the tabulated values of ∆Gf° in Appendix IIB to calculate Ec°ell for the fuel-cell breathalyzer, which employs the following reaction. ((∆G° for HC H O (g) = -374.2 kJ>mol.) CH3CH2OH(g) + O2(g) ¡ HC2H3O2(g) + H2O(g)

440

Draw an electrolytic cell in which Mn2+ is reduced to Mn and Sn is oxidized to Sn2+. Label the anode and cathode, indicate the direction of electron flow, and write an equation for the half- reaction occurring at each electrode. What minimum voltage is necessary to drive the reaction?

959

Calculate E° for each of the following reactions, and tell which are spontaneous under standard-state conditions. (a)

840

Given the following half-reactions and E° values, write a balanced equation for the formation of Mn2+ and MnO2 from Mn3+, and calculate the value of E° for this reaction. Is the reaction spontaneous under standard-state conditions?

1082

Predict whether the following reactions will be spontaneous in acidic solution under standard conditions: (c) reduction of Ce4+ to Ce3+ by H2O2,

1038

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 Breath-alyzer 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?

680

(b) Given the following reduction potentials, calculate the standard emf of the cell: Cd1OH221s2 + 2 e- ¡ Cd1s2 + 2 OH-1aq2 E°red = -0.76 V NiO1OH21s2 + H2O1l2 + e- ¡ Ni1OH221s2 + OH-1aq2 E°red = +0.49 V

1245

You are on your dream vacation at the beach when a major storm knocks out the power for days. Your cell phone is dead, and you want to make a battery to charge it. You find the following materials in the beach house. blue stone algaecide for pools, which can be used to make a 1.0 M Cu2+ solution alum in the kitchen, which can be used to make a 1.0 M Al3+ solution aluminum foil, copper wire, and bologna, which can be used as a salt bridge. (b) What voltage can be generated?

270

229

A storm has knocked out power to your beach house, and you would like to build a battery from household items to charge your iPhone. You have the following materials. alum in the kitchen, which can be used to make a 1.0 M Al3+ solution bleach, which is a solution that is approximately a 1.0 M in ClO-aluminum foil, a platinum necklace and bologna, which can be used as a salt bridge (b) What voltage can be generated?

197

H₂(g) + F₂(g) → 2 H⁺(aq) + 2 F⁻(aq).

114

What species is/are formed at the anode of the alkaline fuel cell?

Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.) 3 Cl₂(g) + 2 Fe(s) → 6 Cl^-(aq) + 2 Fe³⁺(aq) Cl₂(g) + 2 e^- → 2 Cl^-(aq) E° = +1.36 V Fe³⁺(aq) + 3 e^- → Fe(s) E° = -0.04 V

295

Determine E° (cell) for the reaction Al(s) + 3 Ag⁺(aq) → 3 Ag(s) + Al³⁺(aq).

392

What is E° (cell) for the reaction 2 Au(s) + 3 Ca²⁺(aq) → 2 Au³⁺(aq) + 3 Ca(s)?

393