Microsoft PowerPoint - Chapter 8 Lecture2

Microsoft PowerPoint - Chapter 8 Lecture2 - An Alkaline...

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An Alkaline Cell – what’s going on here? Reduction is taking place at the Cathode: 2MnO 2 + H 2 O + 2e - b Mn 2 O 3 + 2OH - Oxidation is taking place at the Anode: Zn + 2OH - b Zn(OH) 2 + 2e - And if we sum these two equations: 2MnO 2 + H 2 O + 2e - b Mn 2 O 3 + 2OH - at cathode (reduction) Zn + 2OH - b Zn(OH) 2 + 2e - at anode (oxidation) We get: Zn + 2MnO 2 + H 2 O b Zn(OH) 2 + Mn 2 O 3 An Alkaline Cell – what’s going on here? • The oxidation half-reaction at the anode sends electrons through the external circuit to power whatever the battery is attached to • After flowing through your i-pod, radio, cell phone or whatever, the electrons return to the battery • The electrons return to the battery through the cathode, where reduction is taking place • This rate at which these electrons flow is called current • Current is measured in amperes (amps) or milliamps for smaller cells • Larger cells can sustain the transfer of electrons for a longer time 8.2 Mercury batteries had the advantage of being very small Used in watches, cameras, hearing aids Toxicity and disposal concerns led to alternatives How well do Batteries Work • Very well! • Li-Iodine batteries in pacemakers can last up to 10 years • Power plants have an efficiency of about 30-40% for converting fuel to electricity • Batteries have an outstanding efficiency of about 90% for converting chemical energy to electricity So why don’t we use Batteries for Everything? Drawbacks? • Even though batteries are very efficient, a considerable amount of energy is expended in making them • Ores and minerals must be mined • The batteries parts must be manufactured • Then they must be assembled • They have a finite life So why don’t we use Batteries for Everything? Drawbacks? • Even rechargeable batteries have to be replaced • In all batteries, electrons eventually cease to flow and they are “dead” • Then, some can be difficult to dispose of due to their chemical content
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8.3 Lead-Acid (Storage) Batteries 8.3 Lead-Acid (Storage) Batteries • Lead batteries are called “storage batteries” • - because they “store” electricity • They are used in almost all automobiles Lead-Acid (Storage) Batteries • The Lead-acid storage battery is a true battery because it consists of six cells,
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Microsoft PowerPoint - Chapter 8 Lecture2 - An Alkaline...

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