CHM102_Chapter 19 class notes

CHM102_Chapter 19 class notes - 1/4/2011 Chapter 19...

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1/4/2011 1 Chapter 19 Electrochemistry Half-Reactions 1. Balancing Oxidation–Reduction Reactions in Acidic and Basic Solutions Voltaic Cells 2. Construction of Voltaic Cells 3. Notation for Voltaic Cells 4. Cell Potential 5. Standard Cell Potentials and Standard Electrode Potentials 6. Equilibrium Constants from Cell Potentials 7. Dependence of Cell Potentials on Concentration 8. Some Commercial Voltaic Cells Contents and Concepts
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1/4/2011 2 Electrolytic Cells 9. Electrolysis of Molten Salts 10. Aqueous Electrolysis 11. Stoichiometry of Electrolysis Electrochemistry The study of the interchange of chemical and electrical energy. Electrochemical processes are oxidation-reduction reactions in which: the energy released by a spontaneous reaction is converted to electricity or electrical energy is used to cause a nonspontaneous reaction to occur
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1/4/2011 3 Oxidation-Reduction Reactions In Chapter 4 we introduced the half-reaction method for balancing simple oxidation-reduction reactions. Oxidation-reduction reactions always involve a transfer of electrons from one species to another. Recall that the species losing electrons is oxidized , while the species gaining electrons is reduced . Oxidation-Reduction Reactions Describing Oxidation-Reduction Reactions An oxidizing agent is a species that oxidizes another species; it is itself reduced . A reducing agent is a species that reduces another species; it is itself oxidized . oxidizing agent reducing agent Loss of 2 e -1 oxidation Gain of 2 e -1 reduction ) ( ) ( 2 ) ( 2 ) ( s aq aq s Cu Fe Cu Fe + + + +
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1/4/2011 4 2Mg ( s ) + O 2 ( g ) 2MgO ( s ) 2Mg 2Mg 2+ + 4e - O 2 + 4e - 2O 2- Oxidation half-reaction (lose e - ) Reduction half-reaction (gain e - ) 0 0 2+ 2- Oxidation number The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. 1. Free elements (uncombined state) have an oxidation number of zero. Na, Be, K, Pb, H 2 , O 2 , P 4 = 0 2. In monatomic ions, the oxidation number is equal to the charge on the ion. Li + , Li = +1 ; Fe 3+ , Fe = +3 ; O 2- , O = -2 3. The oxidation number of oxygen is usually –2 . In H 2 O 2 and O 2 2- it is –1 .
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1/4/2011 5 4. The oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds. In these cases, its oxidation number is –1 . 6. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge on the molecule or ion. 5. Group IA metals are
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This note was uploaded on 03/15/2011 for the course CHE 215 taught by Professor Aboyousef during the Spring '11 term at American University of Sharjah.

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CHM102_Chapter 19 class notes - 1/4/2011 Chapter 19...

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