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UT CH 302 - Lecture notes
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Principles of Chemistry II © Vanden BoutTodayPotentials vs ConcentrationRelationship between ∆G and EElectrolytic CellsForcing the "non-sponteneous" ReactionPrinciples of Chemistry II © Vanden BoutFirst some nomenclatureGalvanic CellVoltaic CellBatterySpontaneous∆G<0E > 0volt meterE>0Anode CathodeCathode at a higher potential than the anodeSo cathode get the PLUS sign+-Principles of Chemistry II © Vanden BoutFirst some nomenclatureElectrolytic CellNon-Spontaneous∆G>0E < 0volt meterE<0Anode CathodeAnode at a higher potential than the cathodeSo anode get the PLUS sign-+Principles of Chemistry II © Vanden BoutIn the following standard Ecell, what is the sign of the cathode?! A.! ! +! B.! ! -! C.! ! neither E°cell = 0Zn(s) | Zn2+ || H+ | H2 (g)Zn2+ + 2e- ---> Zn(s) E° = -0.76 V2H+ + 2e- ---> H2 E° = 0.0 VPrinciples of Chemistry II © Vanden BoutIn the following standard Ecell, what is the sign of the cathode?! A.! ! +! B.! ! -! C.! ! neither E°cell = 0Zn(s) | Zn2+ || H+ | H2 (g)Zn2+ + 2e- ---> Zn(s) E° = -0.76 V2H+ + 2e- ---> H2 E° = 0.0 VE°cell = E°cathode - E°anode = 0 - (-0.76) = +0.76 VVoltaic Cell therefore cathode +Principles of Chemistry II © Vanden BoutWe'll look at standard concentrationsvolt meterX1.1 V1 M Zn2+ (aq) and 1 M Cu2+ (aq) (note this is ridiculously concentrated)Principles of Chemistry II © Vanden BoutWhat about other concentrations?volt meterX?????10-3 M Zn2+ (aq) and 10-1 M Cu2+ (aq) ???Principles of Chemistry II © Vanden BoutRelationship between E and ∆G ∆G is energyE is electrical potentialElectric work (energy) is -charge x potentialwork = -q x E∆G = workmax∆G = - q x EmaxFrom now on well now the Potential we calculate are the theoretical maximumReal world never actually that goodPrinciples of Chemistry II © Vanden BoutRelationship between E and ∆G ∆G = - q x EWhat is the charge q?q = n X Fn is number of moles of electronsF is the charge of one mole of electrons F = 96,485 C (Faraday's Constant)∆G = - nFEPrinciples of Chemistry II © Vanden BoutHow do we measure q in the lab?Current = Charge/TimeAmpere (amp) = Coulomb (C)/ Second (s)If we have the total charge in Coulombwe can figure out how many moles of electrons using FPrinciples of Chemistry II © Vanden BoutYou reduce H+ to H2 in an electrochemical cell.Your cell has a current of 1 Amp for 10 minutesWhat is the total charge that is passed through the cell?! A.! ! 1 C! B.! ! 10 C! C.! ! 600 C! D.! ! 6000 C1 A x (10 min) x (60 s min-1) = 600 CPrinciples of Chemistry II © Vanden BoutYou reduce H+ to H2 in an electrochemical cell.Your cell has a current of 1 Amp for 10 minutesHow many moles of electrons pass through the cell?! A.! ! 600 C / F! B.! ! 600 C x F! C.! ! 1 A x FF is C mol-Therefore the number of moles of electrons is q/FPrinciples of Chemistry II © Vanden BoutYou reduce H+ to H2 in an electrochemical cell.The number of moles of electrons that pass through the cell is 6.2 x 10-3 . How many moles of H2 are formed?! A.! ! 6.2 x 10-3! B.! ! 3.1 x 10-3! C.! ! 1.2 x 10-22H+ + 2e- -----> H2(g)For every mole of H2 you need two moles of electronsPrinciples of Chemistry II © Vanden BoutYou reduce H+ to H2 in an electrochemical cell.Your cell has a current of 1 Amp for 10 minutes. How many moles of H2 are formed?! A.! ! 6.2 x 10-3! B.! ! 3.1 x 10-3! C.! ! 1.2 x 10-22H+ + 2e- -----> H2(g)For every mole of H2 you need two moles of electronsPrinciples of Chemistry II © Vanden BoutOther concentrations and equilibrium∆G = ∆G° + RTlnQat equilibrium ∆G = 0so ∆G° = -RTlnK-nFE = -nFE° + RTlnQE = E° -RTnFlnQE = E° -0.0591nlogQlog!assume 25°CPrinciples of Chemistry II © Vanden BoutWhat about other concentrations?volt meterX?????10-3 M Zn2+ (aq) and 10-1 M Cu2+ (aq) ???Principles of Chemistry II © Vanden BoutZn(s) + Cu2+(aq) Zn2+ (aq) + Cu(s)10-3 M Zn2+ (aq) and 10-1 M Cu2+ (aq) ???Q = [Zn2+][Cu2+]=(10-3)(10-1)= 10-2E = E° -0.0591nlogQE = 1.10 V -0.05912log(10-2) = 1.16VPrinciples of Chemistry II © Vanden BoutE = E° -0.0591nlogQCurrent will flow until E = 0EquilibriumE° = +0.0591nlogKlogK = nE°0.0591Principles of Chemistry II © Vanden BoutConcentration Differences will lead to potential differencePrinciples of Chemistry II © Vanden BoutIf E < 0, then the reaction can be force in the non-spontaneous direction by applying a potential greater than E to the


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UT CH 302 - Lecture notes

Type: Miscellaneous
Pages: 20
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