Principles of Chemistry II © Vanden BoutTodayGalvanic CellsSpontaneous ElectrochemistryPrinciples of Chemistry II © Vanden BoutElectrons have a lower free energy in Zn2+ (and Cu) than Cu2+ (and Zn)Zn Cu2+2 e-Zn2+ CuPrinciples of Chemistry II © Vanden BoutWhich has the lower Standard Gibb's free energy?! A.! ! Zn2+ + Cu! B.! ! Zn + Cu2+! C.! ! They are exactly equal!The reaction will proceed spontaneously tothe lowest free energy sidePrinciples of Chemistry II © Vanden BoutA moment to think again aboutFree Energyand Standard Free Energy∆GDifference in Free Energy between reactants and product under the current conditions (depends on the concentrations of the reactants and products)The concentration will change until ∆G = 0∆G°Difference in Free Energy between reactants and product under standard conditionsstandard conditions are 1 M for all aqueous speciesor 1 atm pressure for all gasesPrinciples of Chemistry II © Vanden BoutLast time, we look at this ideaUse a wire to connect the two sides and have e- flow in an external circuitZn Cu2+2e-Zn2+ Cu Problem, one side is getting more positive one side is getting more negative.We need to keep each side neutralPrinciples of Chemistry II © Vanden BoutAdd a connection that let's a "counter" ion move between the two sidesSO42-ZnZn2+SO42-CuCu2+SO42-2e-As the reaction proceeds Zn is oxidized into Zn2+Cu2+ is reduced into Cunote I have two solid pieces of metal (electrodes)connected to the wirePrinciples of Chemistry II © Vanden BoutPrinciples of Chemistry II © Vanden BoutOxidationZn -> Zn2+ + 2 e-ReductionCu2+ + 2e- -> CuPrinciples of Chemistry II © Vanden BoutNothing will happen as we need to "connect" a circuitPrinciples of Chemistry II © Vanden BoutSalt Bridge or Porous Disk allow ions to flow back and forth between the two beakers. As e- move from one side to the other, counter anions move the opposite directionPrinciples of Chemistry II © Vanden BoutAnode. Oxidation reactionCathode.Reduction ReactionPrinciples of Chemistry II © Vanden BoutHow will I ever remember?AN OX and RED CATANodeOXidationREDuctionCAThodeCathode Ray TubeShoots out electronsPrinciples of Chemistry II © Vanden BoutIn our reaction of Zn goes to Zn2+and Cu2+ goes to CuWhat is the cathode?! A.! ! The Cu strip! B.! ! The Zn strip! C.! ! neither!Reduction at the cathode. Cu2+ is reduced to CuPrinciples of Chemistry II © Vanden BoutIn our reaction of Zn goes to Zn2+and Cu2+ goes to CuIf one mole of Zn dissolves how much Cu is formed?! A.! ! 1 moles! B.! ! 2 moles! C.! ! 0.5 moles!Principles of Chemistry II © Vanden BoutNeed the balanced equationZn Zn2+ + 2e-Cu2+ + 2e- Cu Cu2+ + Zn Cu + Zn2+ One mole of copper for each mole of ZnPrinciples of Chemistry II © Vanden BoutOxidationZn -> Zn2+ + 2 e-ReductionCu2+ -> Cu + 2 e-Principles of Chemistry II © Vanden BoutKw = KaKb = 10-14 (25°C)[H+] = (KaCHA)0.5[H+] = (Ka1Ka2)0.5[H+] = CA[H+] = KA(Ca/Cb)[OH-] = (KbCB)0.5[OH-] = (Kb1Kb2)0.5[OH-] = CB[OH-] = KB(Cb/Ca)[H+]2 - [H+]Ca - Kw = 0[OH-]2 - [OH-]Cb - Kw =
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