batteries and cells
DESCRIPTION
Batteries A battery is a group of cells, connected together in a series (to form more energy)TRANSCRIPT
BATTERIES 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!
• 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)
• 1 Positive electrode = CATHODE• Reduction occurs at the cathode
(GERC)
• 1 Negative electrode = ANODE• Oxidation occurs at the anode
(LEOA)
Voltaic Cells• A voltaic cell is an
arrangement of 2 half cells separated by a porous boundary
Half Cells• A half cell consists of 1
electrode and 1 electrolyte
Half cell Notation
• A half cell can be represented through the following shorthand
Zn(s) ZnSO4(aq) CuSO4(aq) Cu(s)
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)
External Circuit• The connection between the
anode and the cathode through which the electrons travel (metal wire) • Often hooked to an voltmeter
ELECTRICITY• Electricity is
the flow of electrons from the anode to the cathode!!
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)
Energy Potential Difference
• Fancy way of describing the voltage (difference in energy)
• Voltage depends on the chemical composition of the reactants within the cell
Cell Potential = Voltage
• The theoretical voltage can be calculated using the formula:
Ecell = SOA – SRAOr……
Ecell = Cathode - Anode
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.
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?
Electric Current• A measure of the rate of flow
of charge past a point in an electrical circuit
•Measured in Amperes (A)
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)
• 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)
• Remember the SRA gets oxidized at the ANODE!
• Remember the SOA gets reduced at the CATHODE!
• 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- ]
• 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)
• Step 5: draw the cell representation of what is going on, including electron movement
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.
• 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-
• Net reaction
Cu(s) + 2Ag+(aq) Cu2+(aq) + 2Ag(s)
Is this a spontaneous reaction????