Chem 162-2011 Lecture 22

Chem 162-2011 Lecture 22 - CHEMISTRY 162-2011 LECTURE 22...

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Chem 162-2011 Lecture 22 1 CHEMISTRY 162-2011 LECTURE 22 ANNOUNCEMENTS MISCELLANEOUS ATTENDANCE Sign in E-MAIL EXAMS Final exam, Monday, May 9 th , noon – 3 PM Coverage: Chapters 12.1-19.9, 22.7-22.9 QUIZ MISCELLANEOUS
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Chem 162-2011 Lecture 22 2 PLAN FOR TODAY : CHAPTER 17 - ELECTROCHEMISTRY Cover batteries from last lecture 18.8 – Corrosion: Metal loss through voltaic cells 18.9 – Predicting electrolysis reactions 18.10 – Quantitative electrolysis 18.11 – Applications of electrolysis
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Chem 162-2011 Lecture 22 3 * * * *H 2 O half-cell reactions REDUCTION OXIDATION
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Chem 162-2011 Lecture 22 4 G o , E o , K, Interconversions E o cell = E o redn + E o oxidn E cell = E o cell -(RT/nF)ln(Q) = Nernst equation (E cell = E o cell – ((8.314 x 298.15)/(n x 96485)) x (2.303 x log(Q)) E cell = E o cell -(0.0592/n)log(Q) = Nernst equation At equilibrium: 0 = E o cell -(0.0592/n)log(K) E o cell = (0.0592/n)log(K) E cell = (0.0592) x pH G = G o + RT ln(Q) At equilibrium: 0 = G o + RTln(K) G o = -RTln(K) G o = -nFE o cell G = -nFE cell w max = Δ G Definitions: 1 ampere = 1 coulomb of charge/second 1 mole of electrons carries a charge of 1 Faraday = 96485 coulombs Calculations : Amperes x sec x ((Coulombs/sec)/Ampere) x (1 mol e - /96485 coulomb) x (1 mol subst./mol electrons) = mol substance or (amperes x seconds)/(96485 x electronsmol -1 ) = mol substance
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Chem 162-2011 Lecture 22 5 CATCH-UP ON BATTERIES FROM LAST LECTURE Batteries: Using Chemical Reactions to Make Electricity ET note: Fe + O 2 Fe 2 O 3 when the Fe and O 2 are in direct contact. But when kept separate this reaction can generate electricity. Voltaic cell: A device that uses a spontaneous oxidation-reduction reaction to produce electricity. The voltaic cell consists of two half cells. Voltaic cell = Galvanic cell = Battery = a way to spontaneously generate a flow of electrons A voltaic cell converts chemical energy into electrical energy. salt bridge (contains inert ions) Fe 3+ Anode Cathode O 2 bubbling, in solution half cell half cell O 2- in solution Cathode: O 2 (g) + H 2 O(l) + 4e - 4OH - (aq) 0.401 Anode: 2 (Fe(s) Fe 2+ (aq) + 2e - ) 0.440 2Fe(s) + O 2 (g) + 2H 2 O(l) 2Fe 2+ (aq) + 4OH - (aq) 0.841 Electrode: A conductive solid dipped into the solution of an electrochmical cell used to conduct electricity. Electric current: Consists of the electrons going through the Cu wire and the ions moving in the solution. Volt = energy/unit of charge = Joules/coulomb Note: An inert material is used as the electrode in the cathode half cell; this is usally platinum or graphite. Fe Anode Pt Cathode e - anions cations Cu wire e - e - Voltmeter 0.84
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Chem 162-2011 Lecture 22 6 DIFFERENT TYPES OF BATTERIES Dry Cell (primary cells = not rechargeable [because reaction not reversible]) Possible derivation of the word “primary” is that the chemicals are used just one time before they are discarded. Called “dry cell” because it only contains a “moist paste”.
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Chem 162-2011 Lecture 22 - CHEMISTRY 162-2011 LECTURE 22...

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