1. BATTERIES AND CELLS

2. Batteries
A battery is a group of cells, connected together in a series (to form more energy)

3. ELECTRIC CELL
Continuously converts chemical energy into electrical energy
Real life electrochemistry!

4. Each cell is composed of 2 electrodes (solid electrical conductors – usually 2 metals or graphite and metal)
Each cell also contains 1 electrolyte (aqueous electrical conductor)

5. 1 Positive electrode = CATHODE
Reduction occurs at the cathode (GERC)
1 Negative electrode = ANODE
Oxidation occurs at the anode (LEOA)

6. Voltaic Cells
A voltaic cell is an arrangement of 2 half cells separated by a porous boundary

8. Half Cells
A half cell consists of 1 electrode and 1 electrolyte

9. Half cell Notation
A half cell can be represented through the following shorthand
Zn(s) ZnSO4(aq) CuSO4(aq) Cu(s)

10. Porous Boundary
A porous boundary separates the 2 electrolytes, while still permitting ions to move between the 2 solutions (through tiny openings in a salt bridge)

11. External Circuit
The connection between the anode and the cathode through which the electrons travel (metal wire)
Often hooked to an voltmeter

12. ELECTRICITY
Electricity is the flow of electrons from the anode to the cathode!!

13. Voltmeter
A device that is used to measure the energy difference between any 2 points in an electric circuit
Energy is measured in VOLTS (V)

14. Energy Potential Difference
Fancy way of describing the voltage (difference in energy)

15. Voltage depends on the chemical composition of the reactants within the cell

16. Cell Potential = Voltage
The theoretical voltage can be calculated using the formula:
Ecell = SOA – SRA
Or……
Ecell = Cathode - Anode

17. Where Did We Get These #s???
The standard Hydrogen electrode is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials.
It is used to form a basis for comparison with all other electrode reactions, therefore hydrogen’s standard electrode potential is declared to be zero at all temperatures
Potentials of any other electrodes are compared with that of the standard hydrogen electrode at the same temperature.

18. Challenging Diploma Example
If the Ni2+(aq) + 2e-  Ni(s) half reaction is defignated as the reference half reaction with an electrode potential of 0.00V, then what is the electrical potential for the Fe3+(aq) + e-  Fe2+(aq) half reaction?

19. Electric Current
A measure of the rate of flow of charge past a point in an electrical circuit
Measured in Amperes (A)

20. Example:
Write the equations for the half-reactions and the overall reaction that occurs in the following cell:
C(s) Fe2+(aq), Fe3+(aq) Cr2O72-(aq), H+(aq) C(s)

21. Step 1: Label the ALL oxidizing and reducing agents.
Step 2: Find the STRONGEST OXIDIZING AGENT and the STRONGEST REDUCING AGENT
C(s) Fe2+(aq), Fe3+(aq) Cr2O72-(aq), H+(aq) C(s)
SRA = Fe2+
SOA = Cr2O7, H+

22. Remember the SRA gets oxidized at the ANODE!
Remember the SOA gets reduced at the CATHODE!

23. Cr2O72-(aq) + 14H+(aq) + 6e-  2Cr3+ (aq) + 7H2O(l)
Step 3: Write the ½ reactions (from chart or using acid method)
cathode
Cr2O72-(aq) + 14H+(aq) + 6e-  2Cr3+ (aq) + 7H2O(l)
anode
6 [ Fe2+(aq)  Fe3+(aq) + e- ]

24. Cr2O72-(aq) + 14H+(aq) + 6e-  2Cr3+ (aq) + 7H2O(l)
Step 4: Balance electrons and cross out products and reactants to combine reactions
Cr2O72-(aq) + 14H+(aq) + 6e-  2Cr3+ (aq) + 7H2O(l)
6 [ Fe2+(aq)  Fe3+(aq) + e- ]
Cr2O72-(aq) + 14H+(aq) + 6Fe2+(aq)  2Cr3+ (aq) + 7H2O(l) + Fe3+(aq)

25. Step 5: draw the cell representation of what is going on, including electron movement

26. Example 2:
A silver copper voltaic cell consists of a copper half cell with a Cu(s) electrode and a 1.0M Cu(NO3)2 electrolyte, as well as a silver half-cell with an Ag(s) electrode and a 1.0M AgNO3 electrolyte. The 2 half cells are connected by a salt bridge containing KNO3. Write the half reactions and the net reaction.

27. SRA = Cu(s) gets oxidized at the ANODE
SOA = Ag+(aq) gets reduced at the CATHODE
cathode
2 [ Ag+(aq) + e-  Ag(s) ]
anode
Cu(s)  Cu2+(aq) + 2e-

28. Net reaction
Cu(s) + 2Ag+(aq)  Cu2+(aq) + 2Ag(s)
Is this a spontaneous reaction????