Faraday’s Law Of Electrolysis And Classification of cells | Comparison Between Primary And Secondary Cells
Faraday’s Law Of Electrolysis
Faraday’s Law Of Electrolysis First Law
The mass of ions liberated at an electrode is directly proportional to the quantity of electricity charge which passes through the electrolyte
M α Q
m= Mass of ions liberated
Q = Quantity of electricity
Q = It
I = Current
t= time
m α Q
m = ZIt
Z = Z is the constant and is known as the electro equivalant of the substance and it’s unit is Kg/coulomb
Second Law
The mass of ions of different substances liberated by the same quantity of electricity are proportional to their chemical equivalent weights
m α E
E is the equivalent weights of the substance
Chemical equivalent weight = Substance’s atomic weight / Valency
Example
Suppose an electric current is passed for the same time through acidulated water solution of copper sulphate and silver nitrate then for every 1.0078 gram of hydrogen evolved 31.54 gram of copper and 107.88 gram of silver are liberated
The values 107.88 and 31.54 represents the equivalent weight of silver and copper respectively their atomic weights divided by their respective valency
Classification Of Cells
The cells are classified into two types
- Primary cell
- Secondary cell
Primary Cell
A cell which cannot be recharged is called Primary cell. The Primary cells convert chemical energy into electrical energy
Example: Dry cell, Voltaic cell, Daniel cell.In a primary cell, the chemical action is irreversible. The electrodes and the electrolyte undergo changes during discharge which cannot be reversed
Secondary cell
The cell which can be recharged and brought back to the original state is called a Secondary cell
Example : Lead acid cell and Alkaline cells.
The Secondary cell converts electrical energy into chemical energy and it is stored in the cell, during charging. When the cell discharges, the stored chemical energy is converted into electrical energy. These are also known as storage cells. BatteryWhen number of cells are grouped together it is called as battery
Comparison Between Primary And Secondary cell
| SI.NO | Primary cell | Secondary cell |
| 1 | If discharged once cannot be recharged | If discharged can be recharged |
| 2 | If discharged once, cannot be recharged Electrical energy is directly obtained from chemical energy | Electrical energy is first charged in to the cell in the form of chemical energy and then chemical energy is converted into electrical energy |
| 3 | Chemical and electrical factions are irreversible | Chemical and electrical actions are reversible |
| 4 | Low capacity and low efficiency | High capacity and high efficiency |
| 5 | Light in weight | Heavy in weight |
| 6 | Low life | Long life |
| 7 | Low cost and less maintenance | High initial and maintenance cost |
Classification Of Secondary Batteries
Secondary Batteries can be classified into the following categories
Portable Batteries
These are used for starting Lighting and ignition in internal combustion engined vehicles
Example: Lead acid batteries Nickel cadmium batteries
Vehicle Traction Batteries or Motive power
Batteries, or Industrial Batteries.These are used as motive power source for a wide variety of vehicles. Lead-acid batteries, Nickel iron batteries, Silver- Zinc batteries have been used for this purpose. A number of advance batteries including high temperature batteries are under development for electric vehicle (EV) use
Stationary Batteries
Stationary BatteriesThese are classified into two groups
- Standby power system which is used
- intermittently
- Load levelling system which store energy, when
- demand is low and later on, uses it to meet peak demand
