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Electrochemsitry

Electrochemsitry. Relationship between E, Δ G, and K. Relation between E o , ΔG o , and K ΔG = W max amount of useful work done by a reaction system For voltaic or galvanic cell, useful work is produced by the system . - W max = QE Q = charge in coulombs E = voltage

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Electrochemsitry

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  1. Electrochemsitry Relationship between E, ΔG, and K

  2. Relation between Eo, ΔGo, and K ΔG = Wmax amount of useful work done by a reaction system For voltaic or galvanic cell, useful work is produced by the system. -Wmax = QE Q = charge in coulombs E = voltage so ΔG = -QE

  3. 1 mole of electrons = 9.648x104 coulombs so Q = (9.648x104c/mol)(n) ΔG = -(9.648x104 c/mol)(n)(E) ΔG = -nFEor ΔGo= -nFEo

  4. remember that ΔGo = -RTlnK RTlnK = nFEo Eo = RTlnK/nF at 25o C, RT/F = 0.0257 V so Eo = (0.0257 V / n)lnK or ln K = nEo/0.0257 or log K = nEo/0.0592 Note that if Eo is +, ΔGo is -, lnK is +, so K>1

  5. Ex - Find Eo, ΔGo, and K for Cl2(g) + 2 Br-(aq) → 2 Cl-(aq) + Br2(l)

  6. For solutions that are not at 1 M or 1 atm, we need the Nernst Equation. In the expression for Q, gases enter as partial pressures in atmospheres and solutes as concentrations in molarity.

  7. Ex - for the reaction Cl2(g) + 2 Br-(aq) → 2 Cl-(aq) + Br2(l) Calculate the voltage when [Br-] = 1 M, PCl2 = 1 atm and [Cl-] = 0.01 M

  8. Voltage goes up as expected - since the product concentration is low, the reaction should become more spontaneous toward the right. Nernst equation activity

  9. Ex - Consider the reaction Zn(s) + 2 H+ → Zn2+(aq) + H2(g) Suppose[Zn2+] = 1 M, PH2 = 1 atm, find [H+] and pH if the cell potential = 0.460 v.

  10. Notes quiz https://docs.google.com/spreadsheet/embeddedform?formkey=dGIwYVFjdHZVdE15a1FVdDlWM2JuQ2c6MQ

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