General Chemistry Ch 12. Electrochemistry Flashcards
Electrochemical cell
Describes any cell in which oxidation-reduction reactions take place
Electrodes
Strips of metal or other conductive materials placed in an electrolyte solution, electrons flow from anode to cathode, current flows from cathode to anode
Electrolyte
-
Anode
Site of oxidation, attracts anions
Cathode
Side of reduction, attracts cations
Cell diagrams
Shorthand notation that represent the reactions taking place in an electrochemical cell, written from anode to cathode with electrolytes in between, vertical line represents a phase boundary and a double vertical line represents a salt bridge or other physical boundary
Galvanic (voltaic cells)
House spontaneous reactions with a positive electromotive force
Electrolytic cells
House non spontaneous reactions with a negative electromotive force, these non spontaneous cells can be used to create useful products through electrolysis
Concentration cells
Specialized form of galvanic cell in which both electrodes are made of the same material, rather than a potential difference causing the movement of charge, it Is the concentration gradient between the two solutions
Charge of electrodes galvanic cells
Anode is negatively charged and the cathode is positively charged
Charge of electrodes electrolytic cells
Anode is positively charged and the cathode is negatively charged
Rechargeable batteries
Electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states, often ranked by energy density
Charging state
Electrolytic state of rechargeable battery
Discharging state
Galvanic state of rechargeable battery
Energy density
The 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, low energy density
Nickel cadmium batteries (Ni-Cd)
When discharging, consist of a Cd anode and a NiO(OH) cathode in a concentrated KOH solution, when 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, have a higher energy density than lead-acid batteries
Nickel-metal hydride (NiMH)
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
An above average current transiently released at the beginning of the discharge phase, 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 reduction potentials
Ered - Are calculated by comparison to the standard hydrogen electrode under the standard conditions of 298K, 1atm, and 1M
Standard hydrogen electrode
SHE - used for comparison for standard reduction potential calculations, has a standard reduction potential of 0V
Standard electromotive force
Ecell - The difference in the standard reduction potential between the two half cells
Ecell galvanic cells
The difference of the reduction potentials of the two half-reactions is positive
Ecell electrolytic cell
The difference of the reduction potentials of the two half reactions is negative
Electromotive force and free energy
Always have opposite signs
When Ecell+ –> DELTAG - , case in galvanic cells
When Ecell- –> DELTAG+, case in electrolytic cells
When Ecell = 0 –> DELTAG = 0, case of concentration cells
Nernst equation
Describes the relationship between the concentration of species in a solution under nonstandard contains and the electromotive force
Equilibrium and standard electromotive force
When Keq > 1, Ecell +
When Keq <1, Ecell -
When Keq=1, Ecell = 0
