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Reduction Potential and Cells

Reduction Potential and Cells. Define standard electrode potential Calculate standard cell potentials given standard electrode potentials Predict the spontaneity of reactions using standard electrode potentials. Additional KEY Terms. Spontaneous reactions occur without added energy.

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Reduction Potential and Cells

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  1. Reduction Potential and Cells

  2. Define standard electrode potential • Calculate standard cell potentials given standard electrode potentials • Predict the spontaneity of reactions using standard electrode potentials Additional KEY Terms

  3. Spontaneous reactions occur without added energy 2 Ag+(aq) + Cu(s) → Ag(s) + Cu2+(aq) → 2 Ag(s) + Cu2+(aq) no reaction Ag+ions can oxidizeCu metal. Cu2+cannot oxidize Ag metal.

  4. Cell potential (Eocell) • measured in terms of cellvoltage Used to be called Emf – electromotive force • found using electrodereduction potentials • Electrode potentials (Eo) • voltagefrom placing each substance in a cell to compete with hydrogen 2H+(aq) + 2e– ↔ H2(g) Hydrogen was chosen as the “standard”to compare things

  5. (+) Eo • reduced - acceptelectrons fromH+ • X – reduced Hydrogen – oxidized H2(g) / H+(aq) // Cu2+(aq) / Cu(s) Eo = +0.34 V • (-) Eo • oxidized – donated electrons to H+ • X – oxidized Hydrogen – reduced Eo = -0.76 V Zn(s) / Zn2+(aq) // H+(aq) / H2(g)

  6. Reduction Potential Chart (+) means a good “potential” to be reduced – substances likely to take electrons (-) means a bad “potential” to be reduced – substances more likely to give electrons

  7. Cell potential (Eocell) • sumof potentials of each half-cell E°cell = E°ox + E°red Yourtable lists electrode reductionpotentials Oxidationpotentials are the reverse – so we need to switch the sign If… (+) E°cell– spontaneousreaction (-) E°cell– non – spontaneous reaction

  8. What is the cell potential for a silver-copper cell? Ag+(aq) + 1e– → Ag(s) E° = +0.80 V red → Cu(s) – Cu2+(aq) + 2e– E° = 0.34 V ox + The substance with the lowest reduction potential will be oxidized – reverse the reaction and switch the sign on the potential E°cell = E°ox + E°red = - 0.34 + 0.80 + 0.46 spontaneous

  9. For a cell of zinc and gold metal as electrodes: a) What is the cathode and what is the anode?b) What is the cell potential? c) What is the net reaction? d) What is the line notation for the cell?

  10. [ ] ×2 Au3+(aq) + 3e– → Au(s) E° = +1.50 V red [ ] ×3 → Zn(s) Zn2+(aq) + 2e– - E° = 0.76 V ox + + 2.26 E°cell = To write the net reaction you will need to balance the electrons lost and gained Do not multiple the potentials 2 Au3+(aq) + 3 Zn(s) → 2 Au(s) + 3 Zn2+(aq) Zn(s) / Zn2+(aq) // Au3+(aq) / Au(s) (oxidized) (reduced)

  11. 2 Ag+(aq) + Cu(s) → Ag(s) + Cu2+(aq) → 2 Ag(s) + Cu2+(aq) E°c = +0.46 no reaction E°c = - 0.46 You should be able to predict spontaneity by doing the math for the cell potential

  12. Will tin strips in hydrochloric acid react? Sn(s) + H+(aq) → ?? E°c = +0.14 Sn(s) + H+(aq) → Sn2+(aq) + H2(g) 2 Which is reduced and which is oxidized? Will it be spontaneous?

  13. CAN YOU / HAVE YOU? • Definestandard electrode potential • Calculate standard cell potentials given standard electrode potentials • Predict the spontaneity of reactions using standard electrode potentials Additional KEY Terms

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