ELECTROCHEMISTRY Chap 20.

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Presentation transcript:

ELECTROCHEMISTRY Chap 20

Nernst Equation for a Complete Reaction Ecell = E+ − E− = Ecathode − Eanode Only valid when both ½-rxns written as reductions Given: Cd (s) │ Cd(NO3)2 (aq); MA ║ FeCl2 (aq); MC │ Fe (s) [Cd2+] = 0.50 M; [Fe2+] = 0.10 M Ans = −0.058 V (b) [Cd2+] = 0.010 M; [Fe2+] = 1.0 M; Ans = +0.021 V

Calculate the cell potential for: In Class Exercise: Calculate the cell potential for: Cu │ CuCl2 (0.0200 M) ║ AgNO3 (0.0200 M) │ Ag Ans = +0.410 V Calculate the cell potential for: Pt │ UO22+ (0.0150 M); U4+ (0.200 M); H+ (0.0300 M ║ Fe2+ (0.0100 M); Fe3+ (0.0250 M) │ Pt Ans = +0.638 V UO22+ + 4H+ + 2e− → U4+ + 2H2O; Eo = +0.334 V

Applications of Oxidation-Reduction Reactions Batteries and Fuel Cells Corrosion Electrolysis

Batteries Fig 20.19 A 12 V automobile Fig 20.19 Combining cells lead-acid battery Fig 20.19 Combining cells

Fig 20.21 Cutaway view of a miniature alkaline cell

Fig 20.24 Corrosion of iron in contact with water

Fig 20.25 Cathodic protection of iron in contact with zinc

Fig 20.26 Cathodic protection of an iron water pipe Figure 20-26 Title: Cathodic protection of an iron water pipe. Caption: A mixture of gypsum, sodium sulfate, and clay surrounds the magnesium anode to promote conductivity of ions. The pipe, in effect, is the cathode of a voltaic cell. Notes: Keywords:

Fig 20.27 Electrolysis of molten sodium chloride Figure 20-27 Title: Electrolysis of molten sodium chloride. Caption: Cl– ions are oxidized to Cl2(g) at the anode, and Na+ ions are reduced to Na(l) at the cathode. Notes: Keywords: