Electrochemistry Class 12th Notes

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Electrochemistry Class 12th Notes
Electrochemistry Class 12th Notes

Electrochemistry Class 12th Notes | Electrochemistry- Electrochemistry Class 12th easy notes which is easy to learn and understand…

Electrochemistry– Electrochemistry is a branchof chemistry in which relationship between chemical energy and electrical energy and there transformation is studied.

Electrochemical cell– An electrochemical cell is a device in which chemical energy of the redox reaction is converted into electrical energy while electrolytic cell do the  rivers.

Types of electrochemical cells-

Electrochemical cells are of following two types

Electrolytic cell– It is a device in which electrolysis is carried out by using electricity or in which conversion of electrical energy into chemical energy is done. E.g. lead acid battery at the time of charging.

Galvanic cell -It is a device in which a redox reaction is used to convert chemical energy into electrical energy. E.g. daniell, cell lead acid battery at the time of discharging.

Electrode potential– When a metal plate is dipped in the solution of its own ions then potential is developed between metal plates and solution and the metal plate acquire negative or positive charge. This developed potential is known as electrode potential. Electrode potential depends upon the nature of electrode, temperature of solution and concentration of metal ions.

Standard electrode potential – If the concentration of all the ions used  in a half cell is unity, temperature is 25°C and pressure 1 atm then the measured electrode potential is known as standard electrode potential.

Cell potential

In a galvanic cell, the half-cell in which oxidation takes place is called anode and the other half cell in which reduction takes place is called cathode. The potential difference between the two half cells is called the cell potential is measured in volts.

Electromotive force of cell

difference in the electrode potential of two half-cell is known as electromotive force. In standard condition it is known as the standard electrode potential.

Electrochemical series– It is the arrangements of metals in decreasing order of tendency to lose electrons is known as electrochemical series. Sequence of sum of elements present in this series is as follows. Li,K,Na,Mg,Al,Zn,Cr,Fe,Co,Ni ,etc.

Redox potential– When oxidation and reduction reaction occur in a cell comma the potential developed between ions present in metal and solution at equilibrium is known as redox potential. Redox reaction of an element.

\begin{matrix} { M }^{ n+ } \\ Oxidised\quad form \end{matrix}+{ ne }^{ - }\rightarrow \begin{matrix} M \\ Reduced\quad form \end{matrix}

Nernst equation– Equation giving relationship between electric potential and concentration of solution is known as the earnest equation. According to German physicist, Nernst, at a given temperature the relationship between potential of metal electrode, standard electrode potential and concentration of metal ions in solution is given by the relationship

E=E°-\frac { 2.303RT }{ nF } { log}_{10 }\frac { 1 }{ { [M }^{ n+ }] }

Conductance

The ease with which current flows through a conductor is known as its conductance. It is inverse of resistance.

{ C }=\frac { 1 }{ R }

Its unit is ohm { ohm }^{ -1 } or {Ω}^{-1} or  mho

Specific conductance

Reciprocal of specific resistance (p) of a conductor is known as specific conductance (\kappa).

\kappa=\frac { 1 }{ p } =\frac { 1 }{ R } \times \frac { I }{ A }

Unit of specific conductance is { ohm }^{ -1 }{cm}^{-1} or ({S}^ {-1})

Molar conductance ({ \Lambda }_{ m })– Conductance of one mole of electrolyte ions present in a fixed volume of solution is known as molar conductance { \Lambda }_{ m }.

Relationship between molar conductance ({ \Lambda }_{ m })  and specific conductance(\kappa)

{ \Lambda }^{m}=\frac{ \kappa \times 1000}{C}=\frac{ \kappa \times 1000}{M}

where, C or M = molar concentration of solution. Unit of { \Lambda }^{m} is { Siemens}  {m}^{-1}{mol}^{-1}

Equivalent conductance ({\Lambda }_{eq}) Conductance of a solution containing one gram equivalent of an electrolyte is known as equivalent conductance.

relationship between equivalent conductance({\Lambda }_{eq}) and \kappa specific conductance

{ { \Lambda }_{ eq } }=\frac { \kappa  \times  1000 }{ C }

Effect of concentration or dilution on conductance

(a) Effect on specific conductance– On increasing the dilution volume of solution increases but number of Ions does not increase in same ratio. First number of Ions per ml of solution decreases. Since, value of specific conductance depends on number of ions present in per ml of solution has specific conductance of solution decreases.

(b) Effect on molar or equivalent conductance

Specific conductance (\kappa) although decreases with dilution, but the in the value of \kappa is very less as compared to increase in the value of V. Thus, \Lambda and \mu  both increases with dilution.

(c) Solution with infinite dilution

On increasing the dilution the conductance of weak electrolyte increases sharply. Finally a stage is reached when the value of \Lambda and \mu becomes almost constant. Solution at this state is known as solution with infinite dilution.

(d) Kohlrausch’s law of independent Migration of ions

This law states that limiting molar conductivity of an electrolyte can be represented as the sum of the individual contribution of anions and cations of the electrolyte.

Is an electrolyte on this dissociation gives {\nu}_{+}   cations and {\nu}_{-}  anions is limiting molar conductivity is given by

{ \Lambda ° }_{ m }={ \nu }_{ - }{ \lambda ° }_{ + }+{ \nu }_{ - }{ \lambda }_{ - }

Where, { \lambda ° }_{ + }and\quad { \lambda ° }_{ - } are the limiting molar conductivities of the cations and anions respectively and {\nu}_{+} and {\nu}_{-} are the numbers of cations and anions respectively, dilution.

Application of Kohlrausch’s law-
  1. The molar conductivity of weak electrolytes at infinite dilution can be calculated by using Kohlrausch’s law.
  2. Degree of dissociation of weak electrolyte ( like acetic acid ) at a given concentration can be calculated.
  3. Knowing the degree of dissociation ( \alpha ), the dissociation constant(K) of the weak electrolyte at a given concentration of the solution, can be calculated.

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