Electrochemistry Flashcards
electrochemical cell
describes any cell in which oxidation-reduction reactions take place. Certain characteristics are shared between all types of electro chemical cells.
Electrodes
strips of metal or other conductive materials placed in an electrolyte solution.
anode
the site of oxidation. attracts anions . electrons flow from the anode to the cathode.
cathode
the site of reductions. it attracts cations . Current flows from the cathode to anode.
cell diagrams
shorthand notation that represent the reactions taking place in an electrochemical cell. They are written from anode to cathode with electrolytes (the solution) in between. A vertical line represents a phase boundary, and a double vertical line represents a salt bridge or other physical boundary.
Galvanic (voltanic) cells
house spontaneous reactions (ΔG< 0) with a positive electromotive force.
Electrolytic cells
house non spontaneous reactions (ΔG>0) with a negative emf. These cells can be used to create useful products through electrolysis. Chemical compounds are decomposed, any material can be used for electrodes because it is non spontaneous. It just has to be ale to resist the erosion and heat from energy input.
Concentration cells
specialized form of a 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.
The charge on an electrode is dependent on..?
the type of electrochemical cell on is studying.
For galvanic cells, the anode is ___ and cathode is ____?
anode is negatively charged, cathode is positively charged.
For electrolytic cells, the anode is___ and the cathode is ____?
anode is positive and cathode is negative .
Rechargeable batteries are…
electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states. Rechargeable batteries are often ranked by energy density– the amount of energy a cell can produce relative to the mass of battery material.
Lead-acid batters are…?
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 a 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. 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 a higher energy density are more cost effective, and are significantly less toxic.
What is a reduction potential?
quantifies the tendency for a species to gain electrons and be reduced. the higher the reduction potential, the more a given species wats to be reduced.
What is a surge current?
an above average current transiently released at the beginning of the discharge phase; it wanes rapidly until a stable current is achieved.
Standard reduction potentials (E*red)
calculated by comparison to the standard hydrogen electrode force (SHE) under the standard conditions of 298 K, 1 atm pressure, and 1 M concentrations
SHE has a standard reductio potential of …?
0 V .
Standard electromotive force (E*cell)
is the 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 ..?
positive
For electrolytic cells the difference of the reduction potentials of the two half reactions is..?
negative.
EMF and change in free energy always have..?
opposite signs
What is the Nernst equation?
describes the relationship between the concentration of species in a solution under nonstandard conditions and the EMF.
What is the relationship between equilibrium constant (Keq) and E*Cell?
- when Keq (the ratio of products’ concentrations at equilibrium over reactants’, raised to their stoichiometric coefficients) is greater than 1, E*cell is positive.
- when Keq is less than 1, E*cell is negative.
- when Keq is equal to 1, E*cell is 0
Moles of electrons transferred during reduction:
M^n+ + n e- –> M (s)
Electrodeposition equation:
mol M = It/nF . Moles of Metal, IT is Not Fun. M is the amount of metal ion I is the current, t is time, and n is the number of electron equivalents .
Standard electromotive force of a cell equation
Ecell = Ered,cathode - E*red,anode
Standard change in free energy from standard emf equation.
ΔG* = - nFE*cell
Full Nernst equation
E cell = E*cell -RT/nF ln Q
Nernst equation simplified:
Ecell = E*cell - 0.0592/n log Q
Reaction quotient
Q = [C]^c[D]^d / [A]^a[B]^b
Standard change in free energy from equilibrium constant
ΔG* = -RT ln Keq
Free energy change (nonstandard conditions)
ΔG = ΔG* + RT ln Q
AN OX and a RED CAT
the ANode is the site of OXidation; REDuction occurs at the CAThode
What is the point of a salt bridge?
to exchange anions and cations to balance or dissipate newly generated charges.
Electrolysis
REDOX reaction driven by a external voltage source.
What is Faraday’s law?
states that the liberation of gas and deposition of elements on electrodes is directly proportional to then number of electrons being transferred during redox reaction.
What is the Faraday constant?
is the equivalent charge of 1 mole of electrons. it is 96485 C/mol e, but on the test should round to 10^5.
What is Isoelectric focusing?
a technique used to separate amino acids or polypeptides based on their isoelectric points (pI)
How is ΔG* and emf related?
ΔG* = -nFE*cell .
