BATTERIES AND CELLS.
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Transcript of BATTERIES AND CELLS.
![Page 1: BATTERIES AND CELLS.](https://reader035.fdocuments.net/reader035/viewer/2022062401/5a4d1b097f8b9ab059989db0/html5/thumbnails/1.jpg)
BATTERIES AND CELLS
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Batteries• A battery is a group of cells,
connected together in a series (to form more energy)
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ELECTRIC CELL• Continuously converts
chemical energy into electrical energy• Real life electrochemistry!
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• 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)
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• 1 Positive electrode = CATHODE• Reduction occurs at the cathode
(GERC)
• 1 Negative electrode = ANODE• Oxidation occurs at the anode
(LEOA)
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Voltaic Cells• A voltaic cell is an
arrangement of 2 half cells separated by a porous boundary
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Half Cells• A half cell consists of 1
electrode and 1 electrolyte
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Half cell Notation
• A half cell can be represented through the following shorthand
Zn(s) ZnSO4(aq) CuSO4(aq) Cu(s)
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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)
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External Circuit• The connection between the
anode and the cathode through which the electrons travel (metal wire) • Often hooked to an voltmeter
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ELECTRICITY• Electricity is
the flow of electrons from the anode to the cathode!!
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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)
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Energy Potential Difference
• Fancy way of describing the voltage (difference in energy)
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• Voltage depends on the chemical composition of the reactants within the cell
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Cell Potential = Voltage
• The theoretical voltage can be calculated using the formula:
Ecell = SOA – SRAOr……
Ecell = Cathode - Anode
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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.
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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?
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Electric Current• A measure of the rate of flow
of charge past a point in an electrical circuit
•Measured in Amperes (A)
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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)
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• 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)
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• Remember the SRA gets oxidized at the ANODE!
• Remember the SOA gets reduced at the CATHODE!
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• Step 3: Write the ½ reactions (from chart or using acid method)
• cathodeCr2O72-(aq) + 14H+(aq) + 6e- 2Cr3+ (aq) + 7H2O(l)
• anode 6 [ Fe2+(aq) Fe3+(aq) + e- ]
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• 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)
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• Step 5: draw the cell representation of what is going on, including electron movement
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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.
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• SRA = Cu(s) gets oxidized at the ANODE
• SOA = Ag+(aq) gets reduced at the CATHODE
• cathode2 [ Ag+(aq) + e- Ag(s) ]
• anodeCu(s) Cu2+(aq) + 2e-
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• Net reaction
Cu(s) + 2Ag+(aq) Cu2+(aq) + 2Ag(s)
Is this a spontaneous reaction????