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All grade 12 chapters like chapter 1,Atomic Structure and Periodicity Two thousand years ago, ancient Greek philosophers developed a theory of matter that was not based on the experimental evidences. A notable Greek philosopher,namely, Democritus, believed that all matter was composed of very tiny, indivisible particles. He called them atomos. Hence, the word ‘atom’ came from the Greek word atomos, which means uncuttable or indivisible. Chapter 2:Chemical Bonding and Structure INTRODUCTION A chemical bond is the attractive force that binds atoms together in a molecule, or a crystal lattice. After the periodic table and the concept of electron configuration were developed, scientists began to develop ideas about molecules and compounds. Lewis concluded that atoms combine in order to achieve a more stable electron configuration resulting in molecules or compounds. As independent particles, atoms are at relatively high potential energy. Chapter 3:Physical States of matter -solid -Liq
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In all electrochemical methods, the rate of which depend on:at electrode surface (electrode kinetics),2) kinetics of the electron transfer processreach electrode surface (mass transport)1) rate & means by which soluble speciesoxidation & reduction depend on:
c) temperatureb) nature of electrode surfacea) nature of the reaction
(we don’t have much control over #2)
solution)from the electrode out into the bulkfrom the bulk solution to the electrode (orelectroactive species will tend to diffuseconcentration gradient develops and thespecies at the electrode surface, then areaction depletes (or produces) someconcentration gradient. If electrochemicalDiffusion – movement due to a
Diagram for diffusion
zero throughoutProduct (P) issolutionthroughout theconcentrationits maximumanalyte (A) is atturned on the Before power is
And combining with Fick’s First law givesUsing an expression for Conservation of Mass Fick’s Second Law
Solving Fick’s Laws for particular applications Initial Conditions and Boundary Conditionslike electrochemistry involves establishing
the electrode process“bulk solution” unaffected bythe concentration is still C in theelectrode surface at anytime t>0Some distance away from thethe moment power is turned onelectrode surface goes to zero At t>0 the concentration at thesame throughout the solutionstarts, concentration is C & is At t=0 i.e., before experiment
Boundary 2 Boundary 1 Initial
time
i
a function of timedescribes current ashow Cottrell equation Experiment showing
current (i)
begins at V Voltage applied to cell
(^1) where no
stepped up to Vreaction occurs and is
2
in order to react.the electrode surfacematerial must diffuse toCottrell equation sincetime according to theCurrent drops off withcurrent spike results.process to begin and acausing electrode
11
mole per square metre second
mol m
s-^
flux density
j
farad
F
capacitance
C
farad per metre
F m
permittivity
ε
(none)
charge number
z
square metre per second volt
m 2 s^ - V^
mobility
u
Ω S m
V V A m
A C
resistanceconductivity voltagepotential difference
electrical potentialcurrent densitycurrentcharge
ohm
R
siemens per metre
κ ∆ E
volt
∆φ E
volt
φ
ampere per square metre
i
ampere
I
coulomb
Q
Unit
Quantity
Ω (^) F = s second
V C = J joule
note that
a
Layer (Nernst diffusion
δ)
(stagnant solution)
δ
solution)(bulkregionmixing Turbulent
Electrode
Convective Mass Transport
Electrode converts A + e
(^) P at surface
Mass Transport vs Electrode Kinetics
Experimentally rate of electron transfer is Nernst equationwith applied potential as expressed by the- surface concentrations are in equilibrium- current depends only on mass transferfast for many processes so can assume:
Processes which satisfy these assumptions are known as electrochemically
(^) reversible
Ox + e
(^) Red
(^) process more irreversible
overpotential
