1. Electrochemical Cells (Galvanic, Voltaic, Electric)

2. the “half cell” reactions are occurring separately and are joined by a wire the e - transfer occurs through this external circuit the PE difference (voltage) is manifested as usable energy

4. CathodeAnode mass of electrode Solution electrical charge Ions from salt bridge As the cell proceeds: increases  decreases  -ve as Y +  Y+ve as X  X + +ve “cations” -ve “anions”

5. Cell Shorthand Notation eg. For the Zn/Cu cell: Zn│ Zn 2+ ║ Cu 2+ │Cu Conventions: the │ notation indicates a phase boundary where the electrode and electrolyte are in physical contact. the ║ notation represents the salt bridge or porous barrier if additional reactants are required or specific products are formed, they are written with the solution separated by a comma or a semicolon.

6. if the cell has no metal for the electrode, inert electrodes C (s) or Pt (s) are used: Mg │ Mg 2+ ║ MnO 4 ¯, H + ; Mn 2+ │ C (s) standard cells are 1.0 M at SATP all three sets of information – REDOX equation, cell diagram and the cell notation are related and if 1 is provided, the other 2 should be able to be created.

7. Calculating Cell Potential, E°cell  for each half reaction the reduction potential is listed on the chart on p. 805 or the reference sheet.  the complete cell is a combination of the reduction and oxidation half reactions - the sum of the two is the Cell potential, E° cell  this is the usable energy given by: E° cell = E° red (cathode) + E° ox (anode)

8.  as all half reactions are listed as reduction rxns, the oxidation reaction flips the sign, so: E° cell = E° red (cathode) - E° red (anode) eg. Calculate the E° cell for: Br 2 + Cu  2 Br¯ + Cu + ox: Cu  Cu + + e¯ E° ox = -(+0.52) V red: Br 2 + 2 e¯  2 Br¯ E° red = +1.07 V Br 2 + 2 Cu  2 Br¯ + 2Cu + E° cell = + 0.55 V  Spontaneous ( +ve) Or E° cell = +1.07 V – (+0.52 V) = +0.55 V 2x222

9. eg. a)Determine the anode, cathode and calculate the standard cell potential produced by a galvanic cell consisting of a Sn electrode in contact with a solution of Sn 2+ ions and a Cr electrode in contact with a solution of Cr 3+ ions. b)Write the shorthand cell notation. Sn 2+ + 2e-  SnE° = -0.14 V (lesser  flip) Cr 3+ + 3e-  CrE° = -0.74 V Anode:Cr  Cr 3+ + 3e- E° = +0.74 V Cathode:Sn 2+ + 2e-  SnE° = - 0.14 V E cell ° = +0.60 V Cr | Cr 3+ (aq) || Sn 2+ (aq) | Sn

10. eg.Use complete half-reactions and potentials to predict whether the following reaction is spontaneous or non-spontaneous in aqueous solutions. If the cell is spontaneous, write the cell shorthand notation. cat(red): O 2 + 4 H + + 4 e-  2 H 2 O E° = +1.23 V an(ox): 2 SO 2 + 2 H 2 O  2 SO 4 2- + 4 H + + 4 e- E° = -0.18 V E cell ° = +1.05 V O 2 + 2 SO 2 + 4 OH -  2 SO 4 2- + 2 H 2 O 0 -2 +4 +6 | || Pt (s) | SO 2 (g),4 H + ;SO 4 2- (aq)O 2 (g),4 H + ;Pt (s)