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
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

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 is the equiv­a­lent weights of the substance 

Chem­i­cal equiv­a­lent weight = Sub­stance’s atom­ic weight / Valency 


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 

  1. Pri­ma­ry cell 
  2. 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.NOPri­ma­ry cell Sec­ondary cell 
1If dis­charged once can­not be recharged If dis­charged can be recharged
2If dis­charged once, can­not be recharged Elec­tri­cal ener­gy is direct­ly obtained from chem­i­cal energyElec­tri­cal ener­gy is first charged in to the cell in the form of chem­i­cal ener­gy and then chem­i­cal ener­gy is con­vert­ed into elec­tri­cal energy 
3Chem­i­cal and elec­tri­cal fac­tions are irreversibleChem­i­cal and elec­tri­cal actions are reversible
4Low capac­i­ty and low efficiencyHigh capac­i­ty and high efficiency
5Light in weightHeavy in weight
6Low lifeLong life
7Low cost and less maintenance High ini­tial and main­te­nance cost
Com­par­i­son pri­ma­ry and sec­ondary cell

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 

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