AND CELLS Batteries A battery is a group of cells connected together in a series to form more energy ELECTRIC CELL Continuously converts chemical energy into electrical energy Real life electrochemistry ID: 546751
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Slide1
BATTERIES AND CELLSSlide2
Batteries
A battery is a group of cells, connected together in a series (to form more energy)Slide3
ELECTRIC CELL
Continuously converts chemical energy into electrical
energy
Real life electrochemistry! Slide4
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)Slide5
1 Positive electrode = CATHODE
Reduction occurs at the cathode (GERC)
1 Negative electrode = ANODE
Oxidation occurs at the anode (LEOA)Slide6
Voltaic Cells
A voltaic cell is an arrangement of 2 half cells separated by a porous boundarySlide7Slide8
Half Cells
A half cell consists of 1 electrode and 1 electrolyteSlide9
Half cell Notation
A half cell can be represented through the following shorthand
Zn(s
) ZnSO4(aq) CuSO4(aq)
Cu(s
)Slide10
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)Slide11
External Circuit
The connection between the anode and the cathode through which the electrons travel (metal wire)
Often hooked to an voltmeterSlide12
ELECTRICITY
Electricity is the flow of electrons from the anode to the cathode!!Slide13
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)Slide14
Energy Potential Difference
Fancy way of describing the voltage (difference in energy)Slide15
Voltage depends on the chemical composition of the reactants within the cellSlide16
Cell Potential = Voltage
The theoretical voltage can be calculated using the formula:
Ecell
= SOA – SRA
Or……
Ecell
= Cathode - AnodeSlide17
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. Slide18
Challenging Diploma Example
If the Ni
2+
(
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 Fe
3+
(
aq
) + e-
Fe
2+
(
aq
) half
reaction?Slide19
Electric Current
A measure of the rate of flow of charge past a point in an electrical circuit
Measured in Amperes (A)Slide20
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
)Slide21
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
)Slide22
Remember the SRA gets oxidized at the ANODE!
Remember the SOA gets reduced at the CATHODE!Slide23
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
- ]Slide24
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)Slide25
Step 5: draw the cell representation of what is going on, including electron movementSlide26
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.Slide27
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-Slide28
Net reaction
Cu(s
) + 2Ag+(aq)
Cu2+(aq) + 2Ag(s)
Is this a spontaneous reaction????