Transcript Electrochemistry- IMTH II

Electrochemistry
Electrolysis and Electrical Conductance
- Electrolytes and Non-electrolytes
- Electrolysis and it’s mechanism
-Electrical Units
- Coulomb
- Ampere
- Ohm
- Volt
Faraday’s Law of Electrolysis
First Law:
The amount of a given product liberated at an electrode
during electrolysis is directly proportional to the quantity
of electricity which passes through the electrolyte solution.
Second Law:
When the same quantity of electricity passes through
solutions of different electrolytes, the amounts of the
substances liberated at the electrodes are directly
proportional to their chemical equivalents.
The electrical Unit Faraday
The quantity of electricity required to liberate one gram-equivalent
of a substance is 96,500 coulombs. This quantity of electricity is known
as Faraday (F).
1 Faraday = 96, 500 coulombs = 1 Mole electrons
Conductance or Conductivity
The power of electrolytes to conduct electric currents is termed as
conductivity or conductance.
I = E / R, where I= current flow,
E=potential differences at two ends, R=resistance
Specific resistance:
Rαl/A
R = ρ x l/A
Specific conductance:
The conductance of one centimeter cube (cc) of a solution
of an electrolyte.
Κ=1/ρ
Equivalent conductance
The conductance of an electrolyte obtained by dissolving
one gram-equivalent of it V cc of water.
Λ=κxV
Molar conductance
The conduction of all ions produced by one mole
(one gram-molecular weight) of an electrolyte when
dissolved in a certain volume V cc.
μ=κxV
Molar Conductance ( Unit)
Kohlrausch’s Law
The equivalent conductance of an electrolyte at infinite
dilution is equal to the sum of the equivalent conductances
of the component ions.
λ∞ = λa + λc
Ostwald’s Dilution Law
Limitation:
Holds good only for weak electrolytes and fails completely when
applied to strong electrolytes.
Electrochemical Reactions
In electrochemical reactions, electrons are transferred
from one species to another.
Electrochemical Cells
A device for producing an electrical current from a
chemical reaction (redox Reaction) is called an
electrochemical cell.
How a Redox reaction can produce an electrical current?
Electromotive Force (emf)
• Water only
spontaneously flows
one way in a waterfall.
• Likewise, electrons only
spontaneously flow one
way in a redox
reaction—from higher
to lower potential
energy.
• The potential difference between the
anode and cathode in a cell is called the
electromotive force (emf).
• It is also called the cell potential, and is
designated Ecell.
 (cathode) − Ered (anode)
Ecell
 = Ered
Single electrode potential:
The potential of a single electrode in a half-cell
is called the single electrode potential.
Standard EMF of a cell (Eᴼ)
The emf of a cell with 1 M solutions of reactants and products
In solution measured at 25 ᴼC.
Voltaic Cells
A voltaic cell is one in which electrical current is generated
By a spontaneous redox reaction.
- Predicting the oxidizing or reducing ability
- Predicting whether a metal will displace another metal
from it salt or not
THE NERNST EQUATION
Multiple Choice Questions
Question 1. The conductivity of an electrolyte is due to the
a) Presence of ions in the electrolyte
b) free movement of ions in the solution
c) reunion of ions in the solution
d) release of heat energy due to ionisation
Key : (b)
Question2. The electrical conductivity of an electrolyte depends upon
a) The number of molecules in the electrolyte
b) the number of ions present in the electrolyte
c) the number ions present in the solution
d) the number of molecules of the solvent
Key: (c)
Question 3. Ostwald’s dilution law is applicable to
a) All electrolytes
b) strong electrolytes
c) weak electrolytes
d) non-electrolytes
Key (C)
Question 4. The site of oxidation in an electrochemical cell is
a) The anode
b) the cathode
c) the electrode
d) the salt bridge
Key : (a)
Question 5. The salt bridge in the electrochemical cell serves to
a) Increase the rate at which equilibrium is attained
b) increase the voltage of the cell
c) maintain electrical neutrality
d) increase the oxidation/reduction rate
Key : (C)