Chapter 20: Electrochemistry
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Transcript of Chapter 20: Electrochemistry
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CHEMISTRYNinth
Edition GENERAL
Principles and Modern Applications
Petrucci • Harwood • Herring • Madura
Chapter 20: Electrochemistry
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Contents
20-1 Electrode Potentials and Their Measurement
20-2 Standard Electrode Potentials
20-3 Ecell, ΔG, and Keq
20-4 Ecell as a Function of Concentration
20-5 Batteries: Producing Electricity Through Chemical Reactions
20-7 Electrolysis: Causing Non-spontaneous Reactions to Occur
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20-1 Electrode Potentials and Their Measurement
Cu(s) + 2Ag+(aq)
Cu2+(aq) + 2 Ag(s)
Cu(s) + Zn2+(aq)
No reaction
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An Electrochemical Half Cell
Anode
Cathode
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An Electrochemical Cell
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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 ||.
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Terminology
Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
Ecell = 1.103 V
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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-.
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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)
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Standard Hydrogen Electrode2 H+(a = 1) + 2 e- H2(g, 1 bar) E° = 0 V
Pt|H2(g, 1 bar)|H+(a = 1)
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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).
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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
Standard cell potential: the potential difference of a cell formed from two standard electrodes.
E°cell = E°cathode - E°anode
cathodeanode
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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
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Measuring Standard Reduction Potential
anodeanode cathode cathode
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Standard Reduction Potentials
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