1. Electrochemistry
RedOx: Part Deux

2. Electrochemical cells
Voltaic
Converts chemical E from a Favorable RedOx reaction into electrical E
Exothermic reaction
a.k.a. battery
Electrolytic
Uses electrical E to force an UNFAVORABLE RedOx reaction to take place
Endothermic reaction
a.k.a. electroplating

3. Parts of a voltaic (galvanic) cell
anode
more active metal on activity series
½ cell electrode that gets oxidized
will decrease in mass
cathode
½ cell electrode where reduction takes place
will increase in mass
salt bridge
allows for conduction of IONS
Wire
allows for conduction of ELECTRONS

4. half cell half cell Flow of e- Flow of e- Cu Zn anode cathode
salt bridge
Zn Zn+2 + 2e-
Cu+2 + 2e Cu0
IONS
Zn+2
IONS
Cu+2
CuSO4 (aq)
ZnSO4 (aq)

5. Things to remember . . . e- flow Big Reduction Cathode
Anode  Cathode through wire
more active metal  less active metal
Big Reduction Cathode
Anode active Oxidation loses mass
Ions flow across the bridge

7. Half-Cells & Cell Potentials
Electrical potential is a measure of the cell’s ability to produce an electric current.
This results from competition for electrons between two half-cells
E0 = E0red + E0ox

8. Standard Electrode Potentials
Standard Reduction potentials
The more positive the value, the easier the reduction half reaction takes place.
measured in volts

9. How do they know?

10. the reaction is favorable,
When using the formula . …. . switch the sign for oxidation & substitute into the equation
If E0cell is positive,
the reaction is favorable,
Negative is UN
Zero is at equilibrium
(the battery is dead)

11. Fe(s) + Pb2+(aq) --> Fe2+(aq) + Pb(s)
Practice problems
Calculate E0cell for the following reaction
Fe(s) + Pb2+(aq) --> Fe2+(aq) + Pb(s)
Based on E0cell is this reaction favorable?
E0 cell = +0.32V
yes

12. will be the reduction rxn, for the oxidation and ADD.
The more positive
will be the reduction rxn,
THEN SWITCH the sign
for the oxidation and ADD.
What is the maximum cell voltage?
Ag+ + e- --> Ag
Zn+2 + 2e- --> Zn
Is this redox reaction spontaneous?
Ni, Ni+2 // Fe+2, Fe+3

13. UNfavorable RedOx reaction
Electrolytic Cells
UNfavorable RedOx reaction
needs an outside power source to force e- to flow from anode to cathode
Used for electroplating
coating an inexpensive metal with an expensive metal
a.k.a. Electrolysis

14. flow of e-
Cu Cu e-
2e- + Cu Cu0
cathode

16. Similarities & Differences
Both
use RedOx reactions
Anode is site of oxidation
Cathode is site of reduction
e- flow through the wire from anode to cathode
Voltaic Cell
RedOx is favorable
Electrolytic
RedOx is unfavorable
power source necessary
No salt bridge

17. The End