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EGEE 441: Electrochemistry L7
N/A
44
Chemistry
Undergraduate 4
11/27/2012

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Term
how much do transport processes contribute to electrochemical kinetics measurements?
Definition
significantly contribute
Term
transport processes are based on __
Definition
hydrodynamics
Term
hydrodynamics is described with what type of mathematics?
Definition
vector analysis
Term

in eqn 7.1, Ji = -Di*grad(ci) - [zi*F/(R*T)]Di*ci*grad(phi) + ci*v

the first term represents __

Definition
Fickian diffusion
Term

in eqn 7.1, Ji = -Di*grad(ci) - [zi*F/(R*T)]Di*ci*grad(phi) + ci*v

the second term represents __

Definition
migration
Term

in eqn 7.1, Ji = -Di*grad(ci) - [zi*F/(R*T)]Di*ci*grad(phi) + ci*v

the third term represents __

Definition
convection
Term
define potentiostatic regime
Definition
current-time dependence at constant potential
Term
current measurements in the potentiostatic regime can be used to find what 3 things?
Definition
diffusion layer thickness
time dependence of diffusion layer thickness
diffusion coeff. of electrochemically active species
Term
define galvanostatic regime
Definition
current-time dependence at constant current
Term
two key equations for transport processes in electrochem. systems are the __ and __
Definition
flux vector eqn
molar conc. vs time eqn
Term
in order to set up a constant potential so that current density vs. time can be measured, what is needed?
Definition
a 3-electrode system and a potentiostat
Term
under a galvanostatic regime and when the charge-transfer reaction is fast, the conc. gradient at the electrode surface is __
Definition
constant
Term
define transition time
Definition
time to achieve 0 concentration at the electrode surface
Term
list 2 ways that galvanostatic measurements can be used
Definition
1. to define the diffusion coeff. if bulk concentration is known
2. as an analytical tool to measure concentration of the electrochemically active species if the diffusion coeff. is known
Term
galvanostatic measurements can be used to define the diffusion coeff. if...
Definition
bulk concentration is known
Term
galvanostatic measurements can be used as an analytical tool to measure concentration of the electrochemically active species if...
Definition
the diffusion coeff. is known
Term
name 2 ways electrochemical processes can be influenced
Definition
by mass transport due to diffusion
by convection
Term

in eqn 7.7, (∂ci/∂t) = -Di*Lap^2*ci - v*grad(ci)

the first term represents __

Definition
Fickian diffusion
Term

in eqn 7.7, (∂ci/∂t) = -Di*Lap^2*ci - v*grad(ci)

the second term represents __

Definition
convection
Term

for eqn 7.7, (∂ci/∂t) = -Di*Lap^2*ci - v*grad(ci)

it is assumed that when convection in the electrochemical cell is changed, the Nernst diffusion layer is changed or unchanged?

Definition
also changed
Term
cell current depends on hydrodynamics because...
Definition
when convection in the electrochemical cell is changed, the Nernst diffusion layer is also changed
Term
as the intensity of mixing increases, the length of the diffusion layer
Definition
decreases
(more intensive mixing = smaller diffusion layer)
Term
Prandtl layer thickness pertains to velocity of solution or to concentration of the electrochemically active species?
Definition
velocity of solution
Term
Nernst diffusion layer thickness pertains to velocity of solution or to concentration of the electrochemically active species?
Definition
concentration of the electrochemically active species
Term
at the distance below the Prandtl layer thickness, what happens to velocity of the solution?
Definition
velocity begins to drop, reaching zero at the electrode surface
Term
at the distance below the Nernst diffusion layer thickness, what happens to concentration of the electrochemically active species?
Definition
concentration begins to drop, reaching zero at the electrode surface
Term
which typically represents a greater distance from the electrode surface, Prandtl layer thickness or Nernst diffusion layer thickness?
Definition
Prandtl layer thickness
Term
which typically drops faster when approaching the electrode surface, velocity of the solution or the concentration of the electrochemically active species?
Definition
concentration of the electrochemically active species
Term
when solution current is parallel to the electrode surface and perpendicular to the diffusion direction...
Definition
1. Nernst diffusion layer thickness is changing with the length of the electrode
2. the electrode is not equally accessible in the direction of the solution flow
Term
for most systems, if there is mixing of the solution, the Nerst diffusion layer thickness is __
Definition
not known
Term
one of the systems where the Nerst diffusion layer thickness is precisely defined is __
Definition
the RDE
Term
RDE stands for
Definition
rotating disk electrode
Term
what is the main feature of the RDE?
Definition
it is equally accessible at all points on the electrode surface
Term
for the RDE, Nernst diffusion layer thickness depends on what 3 things?
Definition
1. diffusion coeff. of the electrochemically active species
2. viscosity and density of the solution
3. rotation rate of the RDE
Term
for the RDE, the limiting current density can be calculated if...
Definition
the bulk concentration of the electrochemically active species is known
Term
for the RDE, as angular velocity (and hence the rotation rate) of the electrode increases, limiting current density __
Definition
increases (high ang. velocity = high jlim)
Term
for the RDE, if you plot limiting current vs. the square root of angular velocity, the shape of the line is __
Definition
a straight line that goes through the origin
Term
for the RDE, calculating the limiting current density at infinite angular velocity is possible or impossible?
Definition
possible
Term
for the RDE, when angular velocity is infinite, the Nernst diffusion layer thickness equals __
Definition
zero
Term
at high overpotentials, the limiting current...
Definition
is entirely determined by transport processes and is therefore independent of potential
Term
what kind of cell should be used with the RDE?
Definition
a 3-electrode cell
Term
to get high quality data, the RDE should be __
Definition
clean and polished
Term
to study the electrochemical kinetics of a redox reaction, out of what material should the RDE ideally be made?
Definition
platinum
(other materials *can* be used if clean and polished, but Pt is best)
Term
for the RDE, the current density at infinite angular velocity can be used with what equation to calculate exchange current density and symmetry coefficients for the RDE electrochemical reaction?
Definition
Tafel eqn
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