c103-sp10-0524 - Chemistry 103 Spring 2010 Today 1....

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Chemistry 103 Spring 2010 Today 1. Electrochemical cells. Announcements 1. Ch. 14-17 OWL homework is active. 2. CSULA closure on May 31 (holiday). 3. Final exam on Monday, June 7, 4:30 PM. Chapters 14 – 18. Review Balanced redox reactions require atom balance and charge balance. Electrochemical cells require separating the reactants to force an indirect reaction in which electrons flow through an external conductor. Fig. 18.3, p. 654
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Chemistry 103 Spring 2010 2 Electrochemical cells (continued) The anode releases electrons ( – ), and the half- cell fills with more positive ions because of oxidation: Zn(s) Zn 2+ (aq) + 2e - The cathode consumes electrons ( + ), and the half-cell fills loses positive ions because of reduction: Cu 2+ (aq) + 2e - Cu(s) As is, the process will not allow the flow of electrons. The process would create a charge imbalance by trying to generate positive ions in the oxidation half-cell, and by trying to drain positive ions from the reduction half-cell.
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Chemistry 103 Spring 2010 3 To avoid the charge imbalance, the cell needs a salt bridge , which provides excess ions to compensate for generating and draining the ions in the half-cells. Fig. 18.3, p. 654. salt bridge : the component in an electrochemical cell that maintains charge balance within each half-cell; can have various physical forms, but generally it holds a reservoir of solution containing ions, and it allows only the ions to pass freely into the half-cells. Figs. 18.3, 18.5
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Chemistry 103 Spring 2010 4 What is cell voltage? (shown on voltmeter) Cell voltage is a measure of work done per unit of electrical charge. Specifically,
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c103-sp10-0524 - Chemistry 103 Spring 2010 Today 1....

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