Chpt 18 Lec - Chemistry 8/e Steven S Zumdahl and Susan A Zumdahl Chapter 18 Electrochemistry 1 Chapter Contents Balance in acidic and basic

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Chapter 18 Electrochemistry Chemistry 8/e Steven S. Zumdahl and Susan A. Zumdahl 1
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Chapter Contents • Balance in acidic and basic • Galvanic Cells – Cell Potential • Std. Reduction Potential, E° • Electrical Work – Potential and Free Energy, G • E ’s concentration dependence – Nernst Equation – K from E° • Batteries • Corrosion • Electrolysis 2
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Electrochemistry Study of the interchange of chemical and electrical energy Two process involved in oxidation-reduction reaction; e- transfer Generation of electric current from spontaneous chemical reaction Galvanic Cells Its opposite pair; the use of current to produce chemical change Electroplating, electrolysis General Applications; Batteries, anti-corrosion 3
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Oxidation Numbers 4
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What is the oxidation number of U in UO 2 + ? 1. 5 2. 3 3. 1 4. -1 5. -3 6. -5 5
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What is the oxidation number of N in Ca(NO 3 ) 2 ? 1. 5 2. 3 3. 1 4. -1 5. -3 6. -5 6
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What is the oxidation number of S in Na 2 S 2 O 3 ? 1. 6 2. 4 3. 2 4. -2 5. -4 6. -6 7
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Oxidation-Reduction Rxn (Redox) Loss of e- is oxidation Oxidizer is the reducing agent Gain of e- is reduction Reduced is the oxidizing agent • identify what is oxidized and what is reduced Example ; MnO 2 + 4HCl → MnCl 2 + Cl 2 + 2H 2 O 8
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9 Balancing Redox Reactions: Half-Reaction Method Can write half-equations indicating electron transfer The ion or molecule which accepts electrons is called an oxidizing agent (usually non-metallic elements) Metallic elements taking part in redox reactions commonly act as reducing agents Balancing redox equations in solution uses half- reaction Depends on acidity or basicity of solution
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10 Half-Reactions All redox reactions can be thought of as happening in two halves. One produces electrons - Oxidation half. The other requires electrons - Reduction half. Write the half reactions for the following. Na + Cl 2 Na + + Cl - SO 3 - + H + + MnO 4 - SO 4 - + H 2 O + Mn +2
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11 Balancing Redox Equations in Acidic Solution In aqueous solutions the key is the number of electrons produced must be the same as those required. For reactions in acidic solution an 8 step procedure : 1) Write separate half reactions 2) For each half reaction balance all reactants except H and O 3) Balance O using H 2 O
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12 Balancing Redox Equations in Acidic Solution 4) Balance H using H + 5) Balance charge using e - 6) Multiply equation(s) using an integer to make electrons equal 7) Add equations and cancel identical species 8) Check that charges and elements are balanced.
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13 Balance REDOX (Half-Reactions in Acid) Fe +2 (aq) + MnO 4 - (aq) Fe +3 (aq) + Mn +2 (aq) [acid solution]
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Balancing Redox Equations in Basic Solution Do everything you would with acid, but add one more step. Add enough OH
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This note was uploaded on 10/27/2010 for the course CHEM 104 taught by Professor Quigley during the Summer '08 term at CUNY Hunter.

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Chpt 18 Lec - Chemistry 8/e Steven S Zumdahl and Susan A Zumdahl Chapter 18 Electrochemistry 1 Chapter Contents Balance in acidic and basic

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