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Title: electrochemistry
Description: contains....notes..on...diff.. types of cells,,in..electrochemistry.........and...all...phenomenon.in... electrochemistry...from introduction ..
Description: contains....notes..on...diff.. types of cells,,in..electrochemistry.........and...all...phenomenon.in... electrochemistry...from introduction ..
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Chapter 1
...
Reactions involving the
reactant – the electron
...
• Broad Field : electroanalysis, sensors, energy storage
and conversion devices, corrosion, electrosynthesis, and
metal electroplating
...
• These methods make possible the determination of a
particular oxidation state of an element
...
Electrochemical Cells
Electrochemical cells consist of two electrodes: an anode
(the electrode at which the oxidation reaction occurs) and a
cathode (the electrode at which the reduction reaction
occurs)
...
Electrochemical Cells
Conduction
1
...
Solution (ion
migration)
3
...
Electrochemical Potentials
The potential that develops in a cell is a measure of the
tendency for a reaction to proceed toward equilibrium
...
Ref
Eo´
2
...
Electrochemical Potentials
We use concentrations in the Nernst equation, but really
activities are the proper term
...
e
...
Fe+3 + e- ↔ Fe+2 FeCl+2, etc
...
AgCl(s) + e- ↔ Ag(s) + ClE = Eo + (0
...
Hg2Cl2(s) + 2e- ↔ 2Cl- + 2Hg(l)
E = Eo + (0
...
303 RT/F = 0
...
00)//CuSO4 (aCu+2 = 1
...
Electrochemical Cells and Reactions
Electrode (conductor) – Electrolyte (ionic solution)
Electrode
solid
solution
Solution
e-
Ox
Red
Electrodes: Pt, Au, Pd, C, Hg
Ox + e-
Red
Electrolyte solutions (low ohmic resistance):
ionic solutions (NaCl), molten salts, and
ionic polymers (Nafion)
...
Electrochemical Cells and Reactions
Two electrified interfaces but only one of interest
...
Rate of oxidation = Rate of reduction
Reference electrode: AgBr + e-
Ag + Br-(aq) E0 = 0
...
NHE
Electrochemical Cells and Reactions
Magnitude
of
the
potential controls the
direction and rate of
charge transfer
...
Electrochemical Cells and Reactions
• There are two types of current flow:
1
...
Q = nFN
dQ = i = nF dN
dt
dt
2
...
at the electrode-electrolyte
interface
...
Electrochemical Cells and Reactions
Pt/H+, Br- (1M)/AgBr/Ag
(+) current = cathodic
(-) current = anodic
(+) potential = left
(-) potential = right
Br2 + 2e2H+ + 2eEcell = Ec - Ea
2BrH2
E0 = 1
...
NHE
E0= 0
...
NHE
Electrochemical Cells and Reactions
Hg/H+, Br- (1M)/AgBr/Ag
Kinetically fast reactions have
significant faradaic current
flow near Eo, while sluggish
reactions have little current
flow except at large
overpotentials
...
14 V vs
...
00 V vs
...
14 V vs
...
00 V vs
...
Ions move in and out of the interfacial
region in response to potential changes
...
Excess electrons on one
plate and a deficiency on
the other
...
However, the balancing charge on the solution side of the interface
extends out into the solution with some thickness
...
)
Electrified Interfaces
σmetal = -(σIHP + σOHP + σdiffuse)
Structure of the electric double layer has
a major effect on electrode reaction
kinetics! (Faradaic reaction rates)
...
Φ2 – Φs is wasted!!
Φm – Φs is potential felt by analyte
⎛ dy ⎞
Field strength ⎜ dx ⎟ x = x 2 is critical!!
⎝ ⎠
Electrified Interfaces
The solution side of the interface consists of a compact
layer (inner and outer Helmholtz layers) plus a diffuse layer
...
Ionic distribution influenced by ordering due to coulombic
forces and disorder caused by random thermal motion
...
Mass transfer of
reactant/product to and away
from the electrode interface
...
Electron transfer at interface
...
Preceeding or follow-up
chemical reactions
...
Surface processes
(adsorption/desorption)
Working Electrode (Indicator Electrode)
Electrochemical Experiment and Variables in
Electrochemical Cells
η = E - Eeq
dQ
(coulombs/s)
dt
Q (coulombs)
= N (moles electrolyzed)
nF (coulombs/mol)
i (amperes) =
Rate (mol/s) =
dN
dt
=
i
nF
Rate (mol/s-cm2) =
i
nFA
Mass Transport
Modes of Mass Transport
1
...
2
...
3
...
Ji(x) = -Di
Ji(x) = flux of I (mol/s-cm2)
dΦ(x)
= potential gradient
dx
dCi(x)
dx
ziF
RT
dΦ(x)
DiCi
dx
D = diffusion coeff
...
(mol/cm3)
υ(x) = velocity (cm/s)
Mass Transport
l = (2Dt)1/2
Diffusion layer thickness
υmt = Do (dCo/dx)x=0
υmt = Do (C*o – Co(x=0))/δo
Do (C*o – Co(x=0))/δo = i/nFA = Dr(Cr(x=0) – C*r)/δr
Current-Voltage Curve Shapes
Title: electrochemistry
Description: contains....notes..on...diff.. types of cells,,in..electrochemistry.........and...all...phenomenon.in... electrochemistry...from introduction ..
Description: contains....notes..on...diff.. types of cells,,in..electrochemistry.........and...all...phenomenon.in... electrochemistry...from introduction ..