Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION by Steven S. Zumdahl University of Illinois

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Chemistry FIFTH EDITION Chapter 17 Electrochemistry

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Electrochemistry The study of the interchange of chemical and electrical energy. Processes involve Oxidation-Reduction Reactions.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Section 17.5 Batteries A battery is a galvanic cell or, more commonly, a group of galvanic cells connected in series. Read this Section: pages 808 – 813.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Figure One of the Six Cells in a 12-V Lead Storage Battery Anode: Pb Cathode: Pb coated with PbO 2 Electrodes are in a sol’n of H 2 SO 4

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure A Common Dry Cell Battery (Acid Version) Alkaline (Base) Version: KOH or NaOH replaces NH 4 Cl; Last longer than acid version due to less corrosion.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Figure A Mercury Battery Often used in Calculators.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Fuel Cells...galvanic cells for which the reactants are continuously supplied. 2H 2 (g) + O 2 (g)  2H 2 O(l) anode: 2H 2 + 4OH   4H 2 O + 4e  cathode: 4e  + O 2 + 2H 2 O  4OH 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Figure Schematic of the Hydrogen- Oxygen Fuel Cell Apollo missions used such a fuel cell to form water.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Section 17.6 Corrosion Involves oxidation of metals. Oxidation of most metals by oxygen is spontaneous. Oxidation of gold is not spontaneous. Read.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Corrosion Some metals, such as copper, gold, silver and platinum, are relatively difficult to oxidize. These are often called noble metals.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure The Electrochemical Corrosion of Iron Fe 2+ ions formed in the anodic regions travel to the cathodic regions through the moisture on the surface of the steel. There the Fe 2+ ions react with O 2 to form rust.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Figure Cathodic Protection Prevention Of Corrosion Mg is a better reducing agent and will lose e - first.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Section 17.7 Electrolysis...forcing a current through a cell to produce a chemical change for which the cell potential is negative. Electrolytic Cell: uses electrical energy to produce Chemical change.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure (a) A Standard Galvanic Cell (b) A Standard Electrolytic Cell Runs Spontaneously External power source forces electrons through the cell in the opposite direction to that in (a).

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Stoichiometry of Electrolysis 4 How much chemical change occurs with the flow of a given current for a specified time? current and time  quantity of charge  –moles of electrons  moles of analyte  –grams of analyte

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 (a) Coulomb of charge = amps x sec = C x sec sec (b) Mole of electrons = coulombs x 1 mole of e - 96,485 C (c)Moles of metal = mole of e - x mole of metal mole of e - (d) Moles to grams using Molar Mass.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Read Section See Chapter 17 Review.