1. Electrical and Chemical Energy Interconversion
ELECTROCHEMISTRY
Electrical and Chemical Energy Interconversion

2. REDOX REACTION
Reduction
Oxidation
Reducing Agent
Oxidizing Agent

3. ELECTRICAL CONDUCTION
Electrons
Conducting medium
electron transfer (flow)
conductance (mho)
Resistance (ohm)
Copper – solid medium
Aqueous solution – liquid medium

4. Electrochemical Cell e- V Zn Cu ZnSO4 CuSO4 Cl- SALT BRIDGE K+ ANODE
Electrodes – where reaction takes place
OA – CR
Salt bridge – hinder build up of excess positive and negative charges on either solution
Electron movement from anode to cathode
Cl- SALT BRIDGE K+
ANODE
CATHODE

5. ELECTRODES
Active Electrodes
Inert Electrodes

6. CELLS Cell Cell Reaction Ecell GALVANIC SPONTANEOUS + ELECTROLYTIC
NON-SPONTANEOUS -

7. SAMPLE REACTION
Zn(s)  Zn2+ + 2e- 2e- + Cu2+  Cu(s) Zn(s) + Cu2+  Zn2+ +Cu(s) E°cell = E°cathode - E°anode
Based on STANDARD CELL POTENTIAL – standard hydrogen electrode

8. SPONTANEITY
E°cell > 0 SPONTANEOUS at standard state E°cell < 0 NON SPONTANEOUS at standard state w = -nFE ΔG = -nFE ΔG° = -nFE° n = moles of electrons F = Faraday’s constant = C/mole of e-

9. SAMPLE PROBLEM
Evaluate the standard cell potential of each of the following cells and indicate whether the cell is GALVANIC or ELECTROLYTIC.
AuCl4- + Fe2+  Au(s) + 4Cl- +Fe3+
K+ + H2O(l)  O2(g) + H+ + K(s)

10. SEATWORK
Complete the cell reaction for: Pb(s) + MnO4-  Pb2+ + Mn2+ Identify the oxidation and reduction half reaction and evaluate the Standard Cell Potential.

11. CELL REPRESENTATION
Anode | Oxidation || Reduction | Reduction Anode Before Cathode! Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)

12. SEATWORK
5Pb(s) + 16H+ + 2MnO4-  Pb2+ 2Mn2+ +8H2O Write the cell representation for the following reaction.

13. Pt(s) | Fe2+,Fe3+ || Cu2+ |Cu(s)
QUIZ
Pt(s) | Fe2+,Fe3+ || Cu2+ |Cu(s)
Draw the cell. (Include the direction of the flow of electrons)
Identify the half-cell reaction and the complete cell reaction.
Evaluate the standard electron cell potential.
Identify whether the cell is Galvanic or Electrolytic.

14. EFFECT OF CONCENTRATION
ΔG = ΔG° + RT ln Q -nFEcell = -nFE°cell + RT ln Q Ecell = E°cell – RT/nF ln Q At 25°C E = E°cell – /n log Q

15. SAMPLE PROBLEM
Is the cell Pt(s) | Fe2+ (0.10M),Fe3+ (0.06M)|| Cu2+ (0.05M)|Cu(s) Galvanic or Electrolytic?

16. SEATWORK
Is the cell Pb(s) | Pb2+(0.0025M) || H+(0.0020M), MnO4- (0.0030M), Mn2+ (0.010M) | Pt(s) Galvanic or Electrolytic?

17. SAMPLE PROBLEM
Given the cell: Pt | Fe2+, Fe3+ || Mn2+, H+, MnO4- | Pt [Fe2+] = 0.20M [Fe3+] = M [Mn2+] = M [MnO4-] = 0.60M Calculate the pH at which the reaction will occur spontaneously.

18. APPLICATION
On the basis of electrochemistry, provide an explanation on how galvanized iron (iron coated with zinc) prevents corrosion of iron.

19. EVALUATION OF EQUILIBRIUM CONSTANT
ΔG = 0 ΔG = ΔG° + RT ln Q ΔG° = -RT ln Keq -nFE° = -RT ln Keq Keq = e ^ (nFE°/RT) Keq = 10 ^ (nE°/0.0592)

20. SAMPLE PROBLEM
Calculate the Ksp of AgCl AgCl(s) + e-  Ag(s) + Cl-(aq) E°=0.22V Ag(s)  Ag+(aq) + e- E°=0.80V
Ksp = 1.57 x 10^-10

21. Electrical Conduction
Electron / Metallic Conduction – metals
Electrolytic Conduction – salts in solution (electrolytes in general)
Conductance (L) = 1/resistance
Molar conductance (siemens) = 1000Ls/C

22. ELECTROLYSIS - +
A B-

23. MECHANISM OF ELECTROLYSIS
Migration of ions to electrode
Cation to cathode
Anion to Anode
Reaction
Cathode – reduction
Anode - Oxidation

24. FACTORS Nature of Electrodes Nature of Electrolytes Active Inert
Molten (one anion, one cation)
Aqueous (competition )

25. FARADAY’s Law of ELECTROLYSIS
Q = It Q – charge in Coulombs I – current in Ampere t – time in seconds 1 mol of e- carries a charge of 96485C F = C / mol e-

26. SAMPLE PROBLEM
500 C of electricity is applied to a molten solution of NaI.
What are the substances formed at each electrode? Write the reactions.
Determine the mass of products produced.
How about for aqueous solution of NaI?
How about when a current of 10 amperes is applied to molten NaI for 1 hour.

27. SEATWORK
Calculate the mass (if solid) or volume at STP (if liquid) of products from the electrolysis of molten CaCl2 between Platinum electrodes using 5.0A for 8 mins.

28. QUIZ
A spoon with an area of 3.5cm2 is plated with silver from a silver nitrate aqueous solution using a current of 0.60A for 1.6 hours.
How many grams of silver are plated if the current efficiency is 100%? Recalculate for a current efficiency of only 80%.
What is the thickness of the silver plate formed if the density of silver is 10.5 g/cm3?