Slide 1 of 54 CHEMISTRY Ninth Edition GENERAL Principles and Modern Applications Petrucci Harwood Herring Madura Chapter 20: Electrochemistry

Slide 2 of 54 Contents 20-1Electrode Potentials and Their Measurement 20-2Standard Electrode Potentials 20-3E cell, ΔG, and K eq 20-4 E cell as a Function of Concentration 20-5Batteries: Producing Electricity Through Chemical Reactions 20-7Electrolysis: Causing Non-spontaneous Reactions to Occur

Slide 3 of Electrode Potentials and Their Measurement Cu(s) + 2Ag + (aq) Cu 2+ (aq) + 2 Ag(s) Cu(s) + Zn 2+ (aq) No reaction

Slide 4 of 54 An Electrochemical Half Cell Anode Cathode

Slide 5 of 54 An Electrochemical Cell

Slide 6 of 54 Terminology  Electromotive force, E cell.  The cell voltage or cell potential.  Cell diagram.  Shows the components of the cell in a symbolic way.  Anode (where oxidation occurs) on the left.  Cathode (where reduction occurs) on the right. ◦Boundary between phases shown by |. ◦Boundary between half cells (usually a salt bridge) shown by ||.

Slide 7 of 54 Terminology Zn(s) | Zn 2+ (aq) || Cu 2+ (aq) | Cu(s) E cell = V

Slide 8 of 54 Terminology  Galvanic cells.  Produce electricity as a result of spontaneous reactions.  Electrolytic cells.  Non-spontaneous chemical change driven by electricity.  Couple, M|M n+  A pair of species related by a change in number of e -.

Slide 9 of Standard Electrode Potentials  Cell voltages, the potential differences between electrodes, are among the most precise scientific measurements.  The potential of an individual electrode is difficult to establish.  Arbitrary zero is chosen. The Standard Hydrogen Electrode (SHE)

Slide 10 of 54 Standard Hydrogen Electrode 2 H + (a = 1) + 2 e - H 2 (g, 1 bar) E° = 0 V Pt|H 2 (g, 1 bar)|H + (a = 1)

Slide 11 of 54 Standard Electrode Potential, E°  E° defined by international agreement.  The tendency for a reduction process to occur at an electrode.  All ionic species present at a=1 (approximately 1 M).  All gases are at 1 bar (approximately 1 atm).  Where no metallic substance is indicated, the potential is established on an inert metallic electrode (ex. Pt).

Slide 12 of 54 Reduction Couples Cu 2+ (1M) + 2 e - → Cu(s)E° Cu 2+ /Cu = ? Pt|H 2 (g, 1 bar)|H + (a = 1) || Cu 2+ (1 M)|Cu(s) E° cell = V Standard cell potential: the potential difference of a cell formed from two standard electrodes. E° cell = E° cathode - E° anode cathodeanode

Slide 13 of 54 Standard Cell Potential Pt|H 2 (g, 1 bar)|H + (a = 1) || Cu 2+ (1 M)|Cu(s) E° cell = V E° cell = E° cathode - E° anode E° cell = E° Cu 2+ /Cu - E° H + /H V = E° Cu 2+ /Cu - 0 V E° Cu 2+ /Cu = V H 2 (g, 1 atm) + Cu 2+ (1 M) → H + (1 M) + Cu(s) E° cell = V

Slide 14 of 54 Measuring Standard Reduction Potential anode cathode

Slide 15 of 54 Standard Reduction Potentials

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