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MCAT Gen. Chem Ch.12
Term | Definition |
---|---|
Electrochemical Cell | Cell in which oxidation-reduction reactions take place. |
Electrodes | Strips of metal or other conductive materials placed in an electrolyte solution. |
Anode | Site of oxidation, which attracts anions. |
Cathode | Site of reduction, which attracts cations. |
Electrons Flow From: | The anode to the cathode. |
Current Flows From: | The cathode to the anode. |
Cell Diagrams | Shorthand notation that represents the reactions taking place in an electrochemical cell. |
Cell Diagrams Are Written From: | Anode to cathode with electrolytes (the solution) in between |
Vertical Line In Cell Diagrams Represent: | A phase boundary |
Double Vertical Line In Cell Diagrams Represent: | A salt bridge or other physical boundary |
Galvanic (Voltaic) Cells | House spontaneous reactions (Delta G < 0) with a positive electromotive force |
Electrolytic Cells | House nonspontaneous reactions (Delta G > 0) with a negative electromotive force. These nonspontaneous cells can be used to create useful products through electrolysis. |
Concentration Cells | Specialized galvanic cells in which electrodes are made of the same material. This involves a concentration gradient between the two solutions. |
The Charge On An Electrode Is Dependent On: | The type of electrochemical cell one is studying. |
For Galvanic Cells, The Anode Is: | Negatively charged and the cathode is positively charged. |
For Electrolytic Cells, The Anode Is: | Positively charged and the cathode is negatively charged. |
Rechargeable Batteries | Electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states. |
Energy Density | Amount of energy a cell can produce relative to the mass of battery material. |
Lead-acid Batteries When Discharging Consist Of: | A Pb anode and a PbO2 cathode in a concentrated sulfuric acid solution. When charging, the PbSO4- plated electrodes are dissociated to restore the original Pb and PbO2 electrodes and concentrate the electrolyte. |
Lead Acid Batteries Have A Low: | Energy density |
Nickel-Cadmium Batteries (Ni-Cd) When Discharging Consist Of: | A Cd anode and a NiO(OH) cathode in a conc. KOH solution. |
When A Ni-Cd Battery Is Charging: | The Ni(OH)2- and Cd(OH)2- plated electrodes are dissociated to restore the original Cd and NiO(OH) electrodes and concentrate the electrolyte. |
Ni-Cd Batteries Have A Higher Energy Density Than: | Lead-acid batteries |
Nickel-metal Hydrige (NiMH) Batteries Have: | More or less replaced Ni-Cd batteries because they have higher energy density, are more cost effective, and are significantly less toxic |
Surge Current | Above-average current transiently released at the beginning of the discharge phase. It wanes rapidly until a stable current is achieved. |
Reduction Potential | Quantifies the tendency for a species to gain electrons and be reduced. |
The Higher The Reduction Potential: | The more a given species wants to be reduced. |
Standard Electromotive Force (E^ocell) | Difference in standard reduction potential between the two half-cells |
Electromotive Force And Change In Free Energy Always Have: | Opposite signs |
Keq > 1, E^o cell is: | Positive |
Keq < 1, E^o cell is: | negative |
Keq = 1, E^o cell is: | 0 |
Eq. 12.1: Moles of Electrons Transferred During Reduction | M^n+ + n * e- --> M(s). n = moles of electrons |
Eq. 12.2: Electrodeposition Equation | mol M = It / nF. I = current. t = time. n = number of electron equivalents for a specific metal ion. |
Eq. 12.3: Standard Electromotive Force Of A Cell | E^o Cell = E^o red, cathode - E^o red, anode |
Eq. 12.4: Standard Change In Free Energy From Standard emf: | Delta G ^ o = -nFE^o cell. n = number of electron equivalents of a metal ion. F = Faraday constant, 96,485 C / mol e-. |
Eq. 12.5: Nernst Equation (full) | Ecell = E^o cell - RT / nF * ln Q. F = Faraday constant, 96,485 C / mol e-. R = ideal gas constant. R = ideal gas constant, 8.314 j / k*mol. |
Eq. 12.6: Nernst Equation Simplified |