8-2Chapter 8: Energy from Electron TransferFriday September 4, 2009Read: Sections 8.2–8.5 from todaySections 8.6–8.8 for MondayEnd of Chapter Problems:2, 3, 5, 6, 7, 8, 12, 31Overview:I. Basics (Continued)II. Define reduction and oxidation half reactions andoverall cell reactionsIII. Identify structure of common cells and batteriesIV. Hybrid VehiclesV. Fuel CellsChapter 8: Energy from Electron Transfer1. What alternate fuel could be used?2. Fuel alternatives3. What kind of “fuel” is best to be used in cars to better the environment?4. Fuel alternatives – synthesis and use of alternative resources i.e. corn oil5. Is there a way that growth is the use of biofuels will not lead to deforestation?6. What is the chemistry involved with electric car batteries? 7. Will hydrogen fuel ever be possible?8. What is most probably source of energy for the future?Oxidation is loss of electrons: Cd ! Cd2+ + 2e–Cd loses electronsReduction is gain of electrons : 2Ni3+ + 2e– ! 2Ni2+ Ni3+ gains electronsOil Rig is a useful mnemonic device8.1Review: NiCad BatteryOverall cell reaction: 2Ni3+ + Cd ! 2Ni2+ + Cd2+Reality: Electroactive Materials are not mere IonsAnodeCd(s) + OH–(aq) --> Cd(OH)2(s) + ____Cathode2NiO(OH)(s) + 2H2O(l) + 2e– -->2Ni(OH)2(s) + 2OH–(aq)Overall Cell Reaction_____________________________Separator = Water-based paste of KOH or NaOHLaptop battery: http://www.youtube.com/watch?v=tC0UWIYswKIhttp://www.youtube.com/watch?v=FuNSzs679SwRechargeable because all species are solids; need to be ________, _______and ______Text Book Example:What voltage can I get out of a battery built from copper and zinc?Standard Reduction Potentials (Tables of these exist)Cu2+ + 2e– —> Cu(s) E = +0.___ VZn2+ + 2e– —> Zn(s) E = –0.___ VSecret Rule 1: The material with the most _________ standardreduction potential gets oxidized. This means that for a successful battery, we need to start with it being in its reduced form if we ultimately want to oxidize it.e.g., Zn2+/0 redox couple is most negative, so start with it as Zni.e., Zn + Cu2+ —> Zn2+ + ____Determining the Spontaneous Reaction and the VoltageTables of DataHow much voltage can I get?Cu2+ + 2e– —> Cu(s) E = +0.34 VZn2+ + 2e– —> Zn(s) E = –0.76 VConvert to the Galvanic cell formatFollowing rule 1Cu2+ + 2e– —> Cu(s) E = +0.34 VZn —> Zn2+ + 2e–E = _____ VCu2+ + Zn —> Cu + Zn2+E = +1.10 VSecret Rule 2: If you reverse the direction of a reaction, simply _______ the signSecret #3: The reaction is spontaneous as written if E is ______(otherwise, reverse its direction and the sign on E)Worked Example of Calculating VoltagesLab Example of a batteryForce the exchangeof ________ to occurvia an externalelectrical circuit…… and to keep thebalance of ____, allowsalts to cross through a bridge.What happens at the atomic level at the electrode?Atomic Level View of the Galvanic CellWhat do you think the exhausted galvanic cell will look likewhen it has all run out?Zn2e–Zn2+Zn2+Zn2+Zn2+CuCu2+Cu2+Cu2+Cu2+2e–CuZn8.2An ______ Cell8.2 Some Common BatteriesVoltages is defined by the chemical species (increase in series)Current = rate of electron flow (charge passed per unit _____), A(increase in parallel)Lifetime of battery depends upon how much ________ is there• Write half reactions and decide which one gets reversed•!Add 1/2 reactions together for half reactions to get overall cell reaction and voltage. • Positive E values indicate spontaneous in forward direction•!Describe what happens at the microscopic levelGalvanic cellsMany of them form a batteryDraw one of themKnow which are rechargeableReview8.2An ______ Cell8.2 Some Common BatteriesVoltages is defined by the chemical species (increase in series)Current = rate of electron flow (charge passed per unit _____), A(increase in parallel)Lifetime of battery depends upon how much ________ is there8.2Mercury batteries had the advantage of being very _____Used in watches, cameras, hearing aidsToxicity and disposal concerns led to alternatives8.38.3 Lead-Acid Storage BatteriesAnode = PbCathode = PbO2Pb(s) +PbO2(s) + 2 H2SO4(aq) 2 ______(s) + 2 H2O(l)dischargingre-chargingRechargable:This is a true battery as it consists of a series of six cells at __ V = __VDependable and long lasting even against corrosive and weight1) Enclosed spaces and 2) wind turbine back-up storage