Electrochemistry | digitalnotes
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Electrochemical cell(chemical energy to electric energy)
(spontaneous process)
Electrolytic cell(electrical energy to chemical energy)
Electrochemical cell
Note:-
-Electrods are defined by process not by charge.
*oxidation(electrode) taking place - anode
*reduction(electrode) taking place - cathode
Principles of salt bridge(its nutral)
1)used to maintain electrical nutrality @ anode and cathode.
2)used to complete internal curcit
1)Metals electrods--->Anode(Metal[s] | Metal-ions[s]) /
Metal half cell----->cathode(Metal-ion[aq] | Metals[s])
2)Gaseous electrode ---->Anode
(pt[s] | gas | gaseous) / Gaseous half cell------>Cathode (gaseous ion | gas | pt[s] ) (X2(halogen),H2)
Potential Difference
1)electrode potential and 2)cell potential/EMF
Electrode potential -
- between electrode and electrolyte
- cannot be measured with volt meter
- between both the electrodes
- can be measured with voltmeter
Standard Galvanic / Standard voltanic Cell => 1.10V
Electrode potential explanation
SHE (standard hydrogen electrode)
To construct the standard electrode, a platinum wire is diped in acidic soln
and hydrogen gas is passed through it.
The consentration of both oxydised and reduced form is taken as unit(1).
By convention the potential of such an electrode is taken as 0.00V
image
SHE is used to determine standard reduction potential.
Note;-
Which element to find, take it at cathode.
Electrochemical Series
When various elements are arrenged in decreasing order of electrode
potential,(reducing potential) in a series, it is called Electrochemical
series.
Nernst Eqn:- It is used to determine reduction potentials of half cells
when concentration in "not unity"(1M)
for any general rxn
Concentration cell
Potential is generated due to different in concentration at anode and
cathode.
Conductance Measurement
Conductors: METAL
Metallic conductors
Conduct electricity due to the movement of electrons .
No chemical decomposition occurs.
On increasing T,conductance decreases
Electrolytic Conductance
Conduct electricity due to the movement of ions.
chemical decomposition occurs.
AB(s)----> A+(aq) + b-(aq)
On increasing temperature conductance increases.
Ionisation of weak electrolytes
Factors affecting the conductance of electrolytic conductors:-
1.Concentration: concentration inc., conductance decr.
2.Nature of electrolytic: Conductance of strong electrolyte is more than that
of weak electrolyte.
3.Size - Smaller the ions,more will ve the conductance.
4.Temperature: T incr.,Conductance decre.
5.Viscosity:Viscosity increases, conductance decreases.
Conductance Measurement: Ohm's Law
Molar Conductivity(^m)
-Molar Conductivity(^m)-Equivalent Conductivity(^eq)
-Relation b/w ^m & ^eq
nf = no. of replacable H+ ions
Effects of dilution(addition of water)
Strong Electrolytes:-
AB(s)--------> A + B (alpha) ~ 1
On dilution, conductance and molar conductivity increases because inter
- ionic distance increases due to which mobility increases.
^m increases gradually on dilution.
Weak electrolytes
kohlaursch law
Electrolysis
Decomposition of electrolyte on passing electricity.
2.Electrolysis of aquous HCl
3.Electrolysis of dil.H2SO4 solution
4.Electrolysis of concentrated H2SO4
5.Electrolysis of aq CuSO(inert) pt
6.Electrolysis of aq CuSO4 using Cu electrodes
7.Electrolysis of aq NaCl using Hg electrode:
Faraday's 1st law of electrolysis:
Amount of substance diposited is directly proportional to the charge passed.
Faraday's 2nd law of electrolysis:
When same quantity of electricity is passed through the solution of different
electrolytes connected in series,then amount of substance deposited in
directly proportional to their equivalent weight.
Batteries
Primary cells:
Primary Cells are used once & cannot be recharge.
Mercury Cell
Secondary Cell
Can be recharged again by passing current.
Lead - storage Battery
Fule Cell:
Energy is produced by the combustion of H2,CO,CH3H8 etc.
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