Electrochemistry Electrode Potentials
Electrochemistry 1. What are electrode potentials?
Electrochemistry <ul><li>Electric potential arising from the separation of charges in the equilibrium in a redox half equa...
Electrochemistry 2. What can we know from electrode potentials?
Electrochemistry 2. What can we know from electrode potentials?   <ul><li>[Sign] </li></ul><ul><li>  + forward reaction ( ...
Electrochemistry 3. How can we measure standard electrode potentials?
Electrochemistry <ul><li>connect the half cell that you wish to study to the SHE </li></ul><ul><li>Note : </li></ul><ul><l...
Electrochemistry 4. How can we use standard electrode potentials?
Electrochemistry <ul><li>to predict whether a redox reaction is feasible when  2  species are mixed.  </li></ul><ul><li>Ex...
Electrochemistry 4. How can we use standard electrode potentials?   <ul><li>Strategy </li></ul><ul><li>1. Identify possibl...
Electrochemistry Galvanic Cells
Electrochemistry 5. How to distinguish anode and cathode?   Galvanic Cell
Electrochemistry 5. How to distinguish anode and cathode?   Positive     remove electrons    Reduction     Cathode Nega...
Electrochemistry 6. How to draw cell diagram?
Electrochemistry 6. How to draw cell diagram?   Example
Electrochemistry 6. How to draw cell diagram?   <ul><li>Anode || Cathode </li></ul><ul><li>2. Electrodes at the extreme en...
Electrochemistry Electrolytic Cells
Electrochemistry 7. How to distinguish anode and cathode?   Electrolytic Cell
Electrochemistry 7. How to distinguish anode and cathode?   Positive     attract anions    oxidized     Anode Negative ...
Electrochemistry 8. How to predict what species is discharged?   <ul><li>1. Identify all ions in solution (including H 2 O...
Electrochemistry Calculations (Strategy) Question will  surely  involve 1 or more of the formulas: Q = I  t = n F I: curre...
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Electrochemistry

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Electrochemistry

  1. 1. Electrochemistry Electrode Potentials
  2. 2. Electrochemistry 1. What are electrode potentials?
  3. 3. Electrochemistry <ul><li>Electric potential arising from the separation of charges in the equilibrium in a redox half equation. </li></ul><ul><li>It is measured with respect to S.H.E. </li></ul><ul><li>Examples : </li></ul>1. What are electrode potentials? Zn 2+ (aq) + 2e – ⇌ Zn (s) Fe 3+ (aq) + e – ⇌ Fe 2+ (aq) 2H + (aq) + e – ⇌ H 2 (g) Cu 2+ (aq) + 2e – ⇌ Cu (s)
  4. 4. Electrochemistry 2. What can we know from electrode potentials?
  5. 5. Electrochemistry 2. What can we know from electrode potentials? <ul><li>[Sign] </li></ul><ul><li> + forward reaction ( reduction ) favoured </li></ul><ul><li> – backward reaction ( oxidation ) favoured </li></ul><ul><li>[Magnitude] </li></ul><ul><li> – the extent the reaction is favoured </li></ul>
  6. 6. Electrochemistry 3. How can we measure standard electrode potentials?
  7. 7. Electrochemistry <ul><li>connect the half cell that you wish to study to the SHE </li></ul><ul><li>Note : </li></ul><ul><li>You need to be know how to draw the cell setup. </li></ul><ul><li>Things to note when drawing half cell: (1) salt bridge, (2) voltmeter and (3) ensure all gases, solutions are at standard conditions. </li></ul>3. How can we measure standard electrode potentials?
  8. 8. Electrochemistry 4. How can we use standard electrode potentials?
  9. 9. Electrochemistry <ul><li>to predict whether a redox reaction is feasible when 2 species are mixed. </li></ul><ul><li>Examples : </li></ul>4. How can we use standard electrode potentials? I 2 + Cr 2+  feasible? V 3+ + Cu 2+  feasible?
  10. 10. Electrochemistry 4. How can we use standard electrode potentials? <ul><li>Strategy </li></ul><ul><li>1. Identify possible oxidation/ reduction reactions </li></ul><ul><li>Find electrode potentials for these half equations </li></ul><ul><li>Calculate E cell = E red – E ox </li></ul><ul><li>E cell </li></ul><ul><li>+ feasible </li></ul><ul><li>– not feasible </li></ul>
  11. 11. Electrochemistry Galvanic Cells
  12. 12. Electrochemistry 5. How to distinguish anode and cathode? Galvanic Cell
  13. 13. Electrochemistry 5. How to distinguish anode and cathode? Positive  remove electrons  Reduction  Cathode Negative  produce electrons  Oxidation  Anode Electrons flow from A  C Galvanic Cell
  14. 14. Electrochemistry 6. How to draw cell diagram?
  15. 15. Electrochemistry 6. How to draw cell diagram? Example
  16. 16. Electrochemistry 6. How to draw cell diagram? <ul><li>Anode || Cathode </li></ul><ul><li>2. Electrodes at the extreme ends. </li></ul><ul><li>3. Anode: Fe 2+  Fe 3+ </li></ul><ul><li>Cathode: H +  H 2 </li></ul><ul><li>4. If redox species of the same phase, separate by comma; different phase by | </li></ul>Pt (s) | Anode || Cathode | Pt (s) Pt (s) | Fe 2+ Fe 3+ || H + H 2 | Pt (s) Pt(s) | Fe 2+ , Fe 3+ (aq) || H + (aq) | H 2 (g) | Pt(s)
  17. 17. Electrochemistry Electrolytic Cells
  18. 18. Electrochemistry 7. How to distinguish anode and cathode? Electrolytic Cell
  19. 19. Electrochemistry 7. How to distinguish anode and cathode? Positive  attract anions  oxidized  Anode Negative  attract cations  reduced  Cathode Electrons flow from A  C Electrolytic Cell
  20. 20. Electrochemistry 8. How to predict what species is discharged? <ul><li>1. Identify all ions in solution (including H 2 O) </li></ul><ul><li>Cations attracted to cathode; </li></ul><ul><li>Anions attracted to anode </li></ul><ul><li>Find electrode potentials for these half equations </li></ul><ul><li>E ° </li></ul><ul><li>Cathode more positive or less negative is discharged </li></ul><ul><li>Anode more negative or less positive is discharged </li></ul>
  21. 21. Electrochemistry Calculations (Strategy) Question will surely involve 1 or more of the formulas: Q = I t = n F I: current (A) n: moles of electrons! t: time ( s ) F: Faradays constant (96500 C/mol) F = Le L: Avogadro’s constant e: 1.6 x 10 –19 C
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