Important Electrochemistry Formulas for JEE and NEET

Electrochemistry

Electrochemistry cells consist of two half-cells where oxidation and reduction reactions take place. It consists of two electrodes made of metals with different reactivity and due to the difference in electrode potential chemical reactions take place resulting in electrical energy.

Measurement of Electrode Potential

Standard electrode potential is measured using the Standard Hydrogen Electrode (SHE) as a reference.

Cell Potential ( E _cell ) = Cathode Potential (E _cathode ) - Anode Potential (E _anode )

• For any electrode → oxidation potential (O.P) = - Reduction potential (R.P)
• E_cell = R.P of cathode - R.P of anode
• E_cell = R.P. of cathode + O.P of anode
• E_cell is always a positive quantity & Anode will be electrode of low R.P
• E^°_Cell = SRP of cathode - SRP of anode.

Greater the SRP value greater will be oxidising power.

Gibbs Free Energy Change

Nernst Equation

At chemical equilibrium
ΔG = 0 ; E_Cell = 0.

•  
  
  For an electrode M(s)/Mⁿ⁺.
  

Concentration Cell

A cell in which both the electrods are made up of same material.
For all concentration cell E°_cell = 0.
(a) Electrolyte Concentration Cell :
eg. Zn(s) / Zn²⁺ (c₁) || Zn²⁺(c₂) / Zn(s)

(b) Electrode Concentration Cell:
eg. Pt, H₂(P₁ atm) / H⁺ (1M) / H₂(P₂atm) / Pt

Different Types Of Electrodes:

2. Gas-ion Electrode: Pt/H₂(Patm)/H⁺(XM) as a reduction electrode
3. Oxidation-reduction Electrode: Pt / Fe²⁺, Fe³⁺ as a reduction electrode Fe³⁺ + e^- → Fe²⁺
4. Metal-Metal insoluble salt Electrode: eg. Ag/AgCI, Cl^- as a reduction electrode AgCI(s) + e^- → Ag(s) + Cl^-

Calculation Of Different Thermodynamics Function Of Cell Reaction

• ΔG = -n FE_cell
•  (At costant pressure).
• 
• = Temperature cofficient of e.m.f of the cell.E = a + bT + CT² + ....
• 
• ΔCp of cell reaction
  
  

Electrolysis:

Electrolysis is the phenomenon where an electrolyte undergoes decomposition when electricity is passed through its aqueous solution or molten state.In the electrolysis of various electrolytes, two types of electrodes are employed: inert electrodes and active electrodes.

(a)

(b) Similarly the an ion which is strogner reducing agent(low value of SRP) is liberated first at the anode.

Faraday First Law of Electrolysis

Faraday Second Law of Electrolysis

Current Efficiency =

Condition For Simultaneous Deposition Of Cu & Fe At Cathode: 
Condition for the simultaneous deposition of Cu & Fe on cathode.

Conductance:

• 
• Specific conductance or conductivity :
  (Reciprocal of specific resistance) k = 1/ρ K = specific conductance
• Equivalent conductance:
  unit: -ohm^-1 cm² eq^-1
• Molar conductance:
  unit: -ohm^-1 cm² mole^-1
  specific conductance = conductance x l/a

Kohlrausch’s Law:

Variation of λ_eq /λ_M of a solution with concentration :
(i) Strong electrolyte

(ii) Weak electrolytes : where λ is the molar conductivity

n₊ = No of cations obtained after dissociation per formula unit
n_{_} = No of anions obtained after dissociation per formula unit

Application Of Kohlrausch Law:

1. Calculation of λ⁰_M of weak electrolytes :

2. To calculate degree of diossociation of a week electrolyte

3. Solubility (S) of sparingly soluble salt & their K_sp

Ionic Mobility: 

It is the distance travelled by the ion per second under the potential gradient of 1 volts per cm. It’s unit is cm²s^-1v^-1.

Absolute ionic mobility:

Transport Number:

Where t_c = Transport Number of cation & t_a = Transport Number of anion