1. Energy from Electron Transfer (ET)
Batteries
Fuel cells (H2)
Hybrid vehicles
Cellular Electrochemistry (ATP production)
Batteries are a collection of several galvanic cells bundled together
System for direct conversion of chemical energy to electrical energy (spontaneous)
Opposite of electrolytic cell (we will look at this at the end of the unit)

2. LEO the lion says GER
Galvanic cells produce useful energy from redox reactions (electron transfer)
the substances that loses e- or donates the e- is oxidized and is the reducing agent
the substance that gains e- is reduced and is the oxidizing agent
the overall redox reaction can be represented with two balanced half-reactions

3. Corrosion: Common Redox Rxns
Natural redox process that oxidizes metals to their oxides and sulfides (like Fe, Ag, Cu)
Rust
2Fe(s) + 3/2O2(g) + nH2O → Fe2O3·nH2O(s)
Tarnish
develops over Cu, Brass (Cu/Zn alloy), Ag, Al. slower than rust.
caused by chemicals in the air like S.
Bleaching

4. Decide which species is oxidized, which is reduced.
(NiCad battery): 2 Ni3+ + Cd → 2 Ni2+ + Cd2+
2 H2O (l) + Al (s) + MnO4- (aq) → Al(OH)4- (aq) + MnO2 (s)
Balance the second rxn (half reaction method).

5. Construction of Galvanic/Voltaic Cell DEMO: Zn (s) in Cu2+ (aq)
What is happening?
There is ET, but does the system generate electrical energy?
If not, how to make it conduct? How to construct electrochemical cell?

6. Separation of half reactions is the essential idea behind a galvanic/voltaic cell
The two cells are joined by the circuit which consists of a wire and salt bridge
transfer of electrons through an external circuit produces electricity
e- flow is driven by a difference in potential energy, this creates voltage

7. Electrochemical Cells
Both galvanic and electrolytic cells have 3 main parts, 2 electrodes and electrolyte
Electrodes: the objects that conduct the electricity between the cell and the surroundings
Electrolyte: a mixture of ions (usually aq) that are involved in the reaction or that carry the charge.
The electrodes are dipped into the electrolyte

8. Electrodes Anode: the electrode where oxidation takes place (AUTO)
Cathode: the electrode where reduction takes place (CAR)

10. Active vs. Inactive Electrodes
In galvanic cell, e- flows from anode to cathode (e- flow creates voltage)

11. Consider the 2 ½ rxns Zn → Zn2+ + 2e-
ClO H+ + 6 e- → Cl- + 3 H2O
Indicate which reaction occurs at the anode and which at the cathode?
Which electrode is consumed? Inactive or active?

12. Cell Voltage vs. Current
depends primarily on which elements and compounds participate in the reaction
does NOT depend on size of cell, amount of material it contains, or size of the electrodes
DEMO-different size alkaline batteries
Current is the rate of electron flow through an external circuit, measured in amperes (amps, A)
larger cells contain more materials and can sustain ET over a longer period of time

13. How to determine anode material vs. cathode?
Ans: electromotive series
Overall cell potential, standard emf, voltage = Eo
Eocell = Eocath – Eoanode
What’s V for Zn/Cu cell?

14. Al3+ + Mg (s) → Al (s) + Mg2+
Write a balanced eqn.
Determine cell potential.
Do you see trend from electromotive series?
(more neg is easier to oxidize, anode)

15. Strength Questions
If make a voltaic Cell from the following, which is anode? cathode? Eocell?
Cd2+ + 2e- → Cd (-0.40 V)
Sn2+ + 2e- → Sn (-0.14 V)
2. Rank following in order of increasing ability to get reduced
NO3- (Ered = 0.96 V), Ag+ (0.80 V), Cr2O72- (1.33 V)

16. Can H2 reduce Ag+ to Ag?
Pick a reagent that can oxidize Mn to Mn2++ but not oxidize Ni to Ni2+.

17. Thermodynamics Eocell tells something about spontaneity
Recall: rxn is spontaneous if products are favored and energy is released
Determined by H, S, and G (∆G = ∆H -T∆S)
What do you think about sign for Eocell? ∆H ∆S
Spont? - +
Always
low Temp
High Temp
never

18. Cell potential indicates spontaneity
If Eocell is positive, redox is spont.
Spont. reactions can be used to do work (related to ∆Go, where -∆Go is spont.)
Eocell = V = J/C (work/charge)
If system does work, w is negative
At constant T and P, ∆Go = w
Eocell = -w/charge = - ∆Go/charge
1 mol e- can transfer C (Faraday’s constant, F)
Eocell = - ∆Go/nF ∆Go = -nFEo

19. Is rxn spont?
2 NaClO2 (aq) + Cl2 (g) → 2 ClO2 (g) + 2 NaCl (aq)

21. Eocell = - ∆Go/nF ∆Go = -RT lnK Eo = RT lnK = RT lnK nF nF
Prac Ex pg 849
For the reaction, what is the value of n? Calc ∆Go and K at 298 K.
3 Ni Cr(OH) OH-→3 Ni + 2 CrO H2O
Eo = RT lnK = RT lnK
nF nF