Class 12 Chemistry

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Chapter 2- Electrochemistry

Electrochemistry

Electrochemistry is the study of generating Electricity from the energy produced during a spontaneous. chemical reaction.

Electrochemical cells

It is a device in which chemical Energy is converted into Electrical energy and it is also known as electrochemical cells.

Types of electrochemical.cells

TWO types of electrochemical cells are present: Galvanic cells, Electrolytic cells.

(i)Galvanic cells- Galvanic cells which converts Chemical Energy into Electrical energy.

for example-Drycell

(ii)Electrolytic cells- Electrolytic cells which converts Electrical Energy into chemical Energy.

For example-Phone battery

oxidation

(i) Addition of oxygen.

lii) Removal of Hydrogen.

(iii) Loss of Electron.

For example: zn(s)

2+ zn² (2) +2e- (92)+20

Reduction

(i) Addition of Hydrogen.

ii) Removal of oxygen.

(iii) Gain of Electron

For Example: Cu(aq)+2e→ Cu(s)

Redox Reaction

The oxidation and Reduction reaction always occur’s simultaneously in redox reaction or oxidation reduction reaction.

An example of a redox reaction is: PbO ( s ) Lead oxide + H 2 ( g ) Hydrogen → Pb ( s ) Lead + H 2 O ( l ) Water. In the above reaction, hydrogen is oxidized to water and lead oxide is reduced to lead.

Oxidising agent

The substance getting reduced in a chemical reaction is known as the oxidising agent.

Reducing agent

The substance that getting oxidized is known as the reducing agent.

For example, in the given reaction;
H2(g) + F2(g) → 2HF(g)

Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)

Mg(s) + Cu2+ Mg2+ (aq) (aq) + Cu(s)

0

+2

+2

0

Mg(s) is the reducing agent

Cu2+ is the oxidising agent

Electrode

An Electrode is a conductor that is used to make contact with a non-metallic part of a circuit. Electrodes are commonly used in Electrochemical cells.

Electrode potential.

Electrode potential is the voltage of a galvanic cell built form a standard reference Electrode and another electrode to be characterized.

E⁰(Standard Electrode potential)

It can be described as an electrode’s Electrode in comparison to a- Potential measured in Standard hydrogen Electrode under standard conditions. The following are the standard conditions:

(i) A 1M concentration of each ion in the solution.

(ii) A 298k temperature.

(iil) Each gas has a pressure of one bar.

Electrochemical series

The arrangement of elements in order of their Standard reduction potential is called Electrochemical Series. This Electrochemical series is also known as Electromotive force.

Cell potential or EMF of a cell

Cell potential is the difference between the electrode Potentials of two half-cells. If no current is pulled form the cell, it is known as EMF.

E_{cell}=E_{cqthode}+E_{qnode

Nernst Equation Nernst Equation is Relationship between Standard cell Potential and cell potentials.

Ecell Ecell-RT Ing

Ece||=E_{ce||-\frac{0.0591~log~\alpha}{n}log~\alpha

Here Ecell cell potential

Ecell Standard cell potential

Q=product/reactan

R= nas constant (8.314)

T= Temperature (2985) n= no.ofe-participate in reaction.

F= Faradayconstant (96500). (i) log~m^{n}=n~log~m Example- log~10^{6}=6~log~10 log~20^{5}=5~log~20

(ii) log(m\times n)=logm+logn

Example – g~6=log(2\times3)=log~2+log~3

(il) log(m)=logm-log~n value of log log~1=0 log~2=0.301 log~3=0.477 log~4=log~2^{2}=2~log~2=2\times0.301=0.602 log5=0.698 log~6=log(2\times3)=log~2+log~3=0.301+0.477=0.778 log7=0.845 log~8=log~2^{3}=3\overline{x}log~2=3\times0.301=0.903 log~9=log~3^{2}=2\times log3=2\times0.477=0\cdot954 log~10=1 log~100=2.

Electrolysis

Process of decomposition of an Electrolyte when the electric current is passed through its Aqueous or moltenstate.

(i)Faraday first law of Electrolysis The amount of substance deposited or liberated at any electrode, is directly proportional to the quantity of electricity passed through the Electrolyte.

weight of sübstance is directly proportional to Battery deposite

W is directly proportional to Q

W=ZQ

W=Z×I×T

Here w= Amt of substance deposited z= Electrochemical equivalent

I = current

t= time

Electrochemical constantlequivalent (z) Electrochemical constant is defined as the amt of substance deposited on the Electrode when Ic of charge is flow through the solution. #Faraday second law of Electrolysis When the same quantity of current is passed through different Electrolytes which are connected in series, the amt of Substance liberated at respective Electrodes is directly proportional to their equivalent weights.

Given wt. of cu / Given wt. of Na=Equivalent wt. of cu= Equivalent wt. of Na

Equivalent weight = molar mass /valency

Relationship between E⁰cell and kç(Equilibrium constant)

E⁰cell =0.0591 logkc/ n

logkc = nX E⁰cell/ 0.0591. #Relationship between E°cell and ΔG (Gibbs free Energy)

ΔG=–nFE⁰çèĺĺ

Relationship betweenΔGand Kć

ΔG=–2.303RTlogkc

Conductance(C or G)

conductance is the ability of an elements to conduct Electric current.

C=\frac{1}{R}

Here c= conductance

R= Resistance

unit of conductance – Ohm/mho/siemens(s)

Ohm’s law

ohm’s law was given by German Physicist Georg simon ohm. gt states the relationship between current, resistance and voltage across an electrical circuit.

V directly proportional Ì
V=IR
v= voltage
I= current
R= Resistance. #unit of Resistance p= RA = ohm-nt = ohm/m A

Specific conductance or conductivity(k) Specific conductance, also known cis conductivity is a measure of a material’s ability to conduct Electric current.

C=1/ R

K=1/p(rho)

K=1/ohm.m

K= ohm‐¹m‐¹or mho m-¹ or sm‐¹

Relationship between conductance and conductivity

C=1/R

Alc to Resistance

molar conductivity (Am) molar conductivity defined as the conductivity Power of all ions formed by dissolving an Electrolyte mole in a solution

λm = KX1000 /molarity

Here λm=molar conductivity K = conductivity

=Variation of molar conductivity with dilution

=molarconductivity increase because ionic movelity

Kohlrausch law

The limiting molar conductivity Kohlraysch law

The limiting molar conductivity (λ⁰m) of an electrolyte is equal to the sum of the limiting molar conductivity cations (λ⁰+) and (λ⁰-) of the Electrolyte at infinite dilution.

λ⁰m = λ⁰a++λ⁰c

Hereλ⁰m-Limiting molar conductivity or molar conductivity at infinit dilution

Application

1. calculation of molar conductivity of infinite dilution of weak Electrolyte with the help of Strong Electrolyte.
2. Calculate degree of dissociation (α)

α=λm/λ⁰m

3. Dissociation constant of weak Electrolyte (k). K=Cα²/1–α
   Batteries

Batteries is a device that converts chemical energy into electrical Energy.

Types of batteries

1. Primary batteries
2. Secondary batteries

J. Primary batteries primary batteries are single use and cannot be reacharged. Dry cells and most alkaline batteries are examples of primary batteries

2. Secondary batteries

The second type is rechargeable and is called a secondary battery. Example of secondary batteries Phone batteries, include nickel- Cadmium, lead acid and lithium ion batteries