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Chapter 20: Electrochemistry

Petrucci • Harwood • Herring • Madura. GENERAL. Ninth Edition. CHEMISTRY. Principles and Modern Applications. Chapter 20: Electrochemistry. Contents. 20-1 Electrode Potentials and Their Measurement 20-2 Standard Electrode Potentials 20-3 E cell , Δ G , and K eq

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Chapter 20: Electrochemistry

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  1. Petrucci • Harwood • Herring • Madura GENERAL Ninth Edition CHEMISTRY Principles and Modern Applications Chapter 20: Electrochemistry

  2. Contents 20-1 Electrode Potentials and Their Measurement 20-2 Standard Electrode Potentials 20-3Ecell, ΔG, and Keq 20-4Ecell as a Function of Concentration 20-5 Batteries: Producing Electricity Through Chemical Reactions 20-7 Electrolysis: Causing Non-spontaneous Reactions to Occur

  3. Cu(s) + 2Ag+(aq) Cu(s) + Zn2+(aq) No reaction Cu2+(aq) + 2 Ag(s) 20-1 Electrode Potentials and Their Measurement

  4. An Electrochemical Half Cell Anode Cathode

  5. An Electrochemical Cell

  6. Terminology • Electromotive force, Ecell. • 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 ||.

  7. Terminology Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s) Ecell = 1.103 V

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

  9. 20-2 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)

  10. Standard Hydrogen Electrode 2 H+(a = 1) + 2 e- H2(g, 1 bar) E° = 0 V Pt|H2(g, 1 bar)|H+(a = 1)

  11. 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).

  12. Reduction Couples Cu2+(1M) + 2 e-→ Cu(s) E°Cu2+/Cu = ? Pt|H2(g, 1 bar)|H+(a = 1) || Cu2+(1 M)|Cu(s) E°cell = 0.340 V anode cathode Standard cell potential: the potential difference of a cell formed from two standard electrodes. E°cell = E°cathode -E°anode

  13. Standard Cell Potential Pt|H2(g, 1 bar)|H+(a = 1) || Cu2+(1 M)|Cu(s) E°cell = 0.340 V E°cell = E°cathode -E°anode E°cell = E°Cu2+/Cu -E°H+/H2 0.340 V = E°Cu2+/Cu -0 V E°Cu2+/Cu = +0.340 V H2(g, 1 atm) + Cu2+(1 M) → H+(1 M) + Cu(s) E°cell = 0.340 V

  14. Measuring Standard Reduction Potential anode cathode cathode anode

  15. Standard Reduction Potentials

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