Ch 12: Electrochemistry Flashcards
electrochemical cell
any cell in which oxidation-reduction reactions take place. Certain characteristics are shared between all types of electrochemical cells
Electrodes
strips of metal or other conductive materials placed in an electrolyte solution
anode
always site of oxidation. it attracts anions
cathode
always the site of reduction. it attracts cations
electrons flow from ____ to ____
anodes
cathodes
current flows from ____ to ____
cathode
anode
cell diagrams
shorthand notation that represents the reactions taking place in an electrochemical cell
cell diagrams are written from anode to cathode with ____ in between
electrolytes (the solution)
a vertical line represents a ____, and a double vertical line represents a ____ or other physical boundary
phase boundary
salt bridge
galvanic (voltaic) cells
house spontaneous reactions (delta G
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 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 two solutions
charge of an electrode is dependent on
type of electrochemical cell one is studying
for galvanic cells, anode is neg and cathode is pos
for electrolytic cells, anode is pos and cathode is neg
rechargeable batteries
electrochemical cells that experience charging (electrolytic) and discharging (galvanic) states
often ranked by energy density, the amount of energy a cell produces 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. these cells have 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, Ni(OH)2- and Cd(OH)2- plated electrodes are dissociated to restore the original Cd and NiO(OH) electrodes and concentrate the electrolyte. these cells have a higher energy density than lead-acid batteries
nickel-metal hydride (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 reduction potentials (Enot,red) are calculated by comparison to the ____ under standard conditions ____
standard hydrogen electrode (SHE)
298K, 1 atm pressure, 1 M concentrations
standard hydrogen electrode has a standard reduction potential of
0V
Standard electromotive force (Eknot, cell)
difference in standard reduction potential between the two half-cells
for galvanic cells, the difference of the reduction potentials of the two half-reactions is ____; for electrolytic cells, the difference of the reduction potentials of the _____ is negative
positive
two half-reactions
electromotive force and ____ always have opposite signs
change in free energy
