36. Metallic conductor depend upon
• Nature and structure of metal.
• No. of valence electron per atom.
• Temperature of the sample.
37.
38.
39.
40. conductivity aqueous solution
depend upon
• Nature of electrolyte.
• Size of ion.
• Solvation of ion.
• Concentration of electrolytic.
• Temperature.
41.
42.
43.
44.
45.
46.
47.
48. One cell const. and resistivity
Known then we can find value
Easily.
66. 2. Voltaic or Galvanic cells-
An electrochemical cell in which a spontaneous
reaction produces electricity.
Eg. Dry cell, lead storage cell etc.
67. 1. Electrolytic cell-
An electrochemical cell in which a non spontaneous
reaction is forced to occur by passing a direct
current from an external source into the solution.
Eg. Refining metal(purify), electroplating &
production of many chemical substance.
69. Cell Notation
1. Anode
2. Salt Bridge
3. Cathode
Anode | Salt Bridge | Cathode
| : symbol is used whenever there is a different phase
70. 19.2
Cell Notation
Zn (s) + Cu2+
(aq) Cu (s) + Zn2+
(aq)
[Cu2+
] = 1 M & [Zn2+
] = 1 M
Zn (s) | Zn2+
(1 M) || Cu2+
(1 M) | Cu (s)
anode cathode
Zn (s)| Zn+2
(aq, 1M)| K(NO3) (saturated)|Cu+2
(aq, 1M)|Cu(s)
anode cathodeSalt bridge
More detail..
72. Electrochemical Cells
19.2
The difference in electrical
potential between the anode and
cathode is called:
• cell voltage
• electromotive force (emf)
• cell potential
000
reductionoxidationCell EEE +=
UNITS: Volts Volt (V) = Joule (J)
Coulomb, C
73. Standard Electrode Potentials
19.3
Standard reduction potential (E0
) is the voltage associated with a
reduction reaction at an electrode when all solutes are 1 M and
all gases are at 1 atm.
Ε0
= 0 V
Standard hydrogen electrode (SHE)
2e−
+ 2Η+
(1 Μ) Η2 (1 atm)
Reduction Reaction
74.
75. Determining if Redox Reaction is Spontaneous
• + E°CELL ; spontaneous
reaction
• E°CELL = 0; equilibrium
• - E°CELL; nonspontaneous
reaction
More positive E°CELL ;
stronger oxidizing agent or
more likely to be reduced
76. Relating E0
Cell to ∆G0
ech
work
ECell
arg
=
Units
work, Joule
charge, Coulomb
Ecell; Volts
charge = nF
Faraday, F; charge on 1 mole e-
F = 96485 C/mole
work = (charge)Ecell = -nFEcell
∆G = work (maximum)
∆G = -nFEcell
77. Relating Εο
CELL to the
Equilibrium Constant, K
∆G0
= -RT ln K
∆G0
= -nFE0
cell
-RT ln K = -nFE0
cell
K
nF
RT
ECell ln0
=
( )
0257.0
96485
29831.8
=
=
mole
C
K
molK
J
F
RT
K
n
K
n
ECell log
0592.0
ln
0257.00
==
91. Fuel Cell vs. Battery
• Battery; Energy storage device
– Reactant chemicals already in device
– Once Chemicals used up; discard (unless rechargeable)
• Fuel Cell; Energy conversion device
– Won’t work unless reactants supplied
– Reactants continuously supplied; products continuously
removed
92. Fuel Cell
A fuel cell is an
electrochemical cell
that requires a
continuous supply of
reactants to keep
functioning
Anode:
Cathode: O2 (g) + 2H2O (l) + 4e-
4OH-
(aq)
2H2 (g) + 4OH-
(aq) 4H2O (l) + 4e-
2H2 (g) + O2 (g) 2H2O (l)
93. Types of Electrochemical Cells
• Voltaic/Galvanic Cell; Energy released
from spontaneous redox reaction can be
transformed into electrical energy.
• Electrolytic Cell; Electrical energy is used
to drive a nonspontaneous redox reaction.
Oxidation means the loss of electrons (it does not always involve oxygen). Reduction means the gain of electrons (gaining of negatives, that is electrons, reduces the oxidation number of an atom.
When something oxidise another reduce. Electron one loose one accept. Oxidation cannot occure without reduction. Same aa ulta. I nan electrochemical cell both oxidation and reduction occur.
Resistivity (ρ) is defined as the electrical resistance when a sample is 1metre long with a cross-section of 1square metre. Resistivity is measured in ohm-metres.
R = ρ l/AIf l = 1m and A = 1m2 R = ρ 1m/1m2 R = ρ
Conductivity (κ) is the conductance of a material when it is 1metre long with a cross section of 1square metre. Conductivity is
Rbefore going to study conductivity of chemical cell first understand some key term.If l = 1m and A = 1m2 R = ρ 1m/1m2 R = ρ
Conductivity (κ) is the conductance of a material when it is 1metre long with a cross section of 1square metre. Conductivity is
Electrical resistance of any current is directly proportional to l and A.
SI unit of resistivity is given 2nd point.
Conductance is inverse of resisitance.
Conductivity is donted by k called kappa. Greek
Denpending on there conductivity material are classified as conductore insulator semiconductor
Apart from this conductor there is one more conductor is called zero conductor.
Some metal alloy become super conductor at lower temperature. And some mix oxide at high temperature show super conductor.
Let us discuss about conductance electric conductance thrugh metal.
Metallic conductor depend upon
Conductivity also occure in pure water.
Pure water contain very less oh ion bcose of this pure water is very low conductivity.
By putting ioin concductivity increase.
To measure the ionic conductivity cell we use cell .
To calculate the distance btween two area is very difiicult. The column of the solution seperating the two electrode then has a resistance describe by eqn givwen.
G star show there cross section area.
If there is no conductivity we measure by resistance of the condcutivity.
Measurement of conductivity we can use witston bridge. Variable resistance R1. p detector show current flow. R2 is unknown resistance. O show AC power supply.
When the bridge balance no flow though the detector. At this condition equation is R2=
Measure conductivity of solution and resistance of cell. One cell constant and resistivity known then.
We converting the unit result gets second equation.
As solution diluted only few ions remain that’s why decrease conductivity.
Strong electrolyte kam ion se bhi electricity conduct karega. But weak electrolyte already weak hai to wo electiricity conduct nahi karpayga.