Tamilnadu Samacheer Kalvi 12th Chemistry Notes Chapter 9 Electro Chemistry Notes
Electro chemistry : The branch of chemistry that deals with the study of electrical energy transport and the inter conversion of electrical and chemical energy is called electro chemistry.
Ohm’s law : At a constant temperature, the current flowing through the cell (I) is directly proportional to the voltage across the cell (V)
I ∝ V
(OR)
I = V/R
(OR) V = IR
Resistivity: Resistance of an electrolytic solution is directly proportional to the length (1) and inversely proportional to the cross sectional area (A)
R ∝ l/A
Conductivity: The reciprocal of the resistance gives the conductance of an electrolytic solution.
C = 1/R
Specific conductivity: The reciprocal of the specific resistance
(OR)
The conductance of a cube of an electrolytic solution of unit dimensions are called specific conductance.
\(\kappa=\frac{1}{\rho} \cdot \frac{l}{A}\)
Molar conductivity (∧m): It is defined as the conductance of a solution containing one mole of the electrolyte dissolved in it.
\(\Lambda_{\mathrm{m}}=\frac{\kappa \times 10^{-3}}{\mathrm{M}} \mathrm{sm}^{-1} \mathrm{~m}^{3} \mathrm{~mol}^{-1} \text {(or) } \mathrm{mho} \mathrm{m}^{3} \mathrm{~mol}^{-1} \text {. }\)
Equivalent conductance (∧): It is defined as the conductance of an electrolyte solution containing one gram equivalent of the electrolyte.
\(\Lambda=\frac{\kappa \times 10^{-3}}{N} \mathrm{sm}^{-1} \mathrm{~m}^{3}\)
(gram equivalent)-1 (or) mhom3 (gram equivalent)-1.
Kohlraush’s law: At infinite dilution, the limiting molar conductivity of an electrolyte is equal to the sum of the limiting of molar conductivities of its constituent ions.
Application of Kohlraush’s law: Kohlraush’s law used as,
- Calculation of molar conductance at infinite dilution of a weak electrolyte.
- Calculation of degree of dissociation of weak electrolytes.
- Calculation of solubility of a sparingly soluble salts.
Electro chemical cell: It is a device which inter converts chemical into electrical energy and vice versa.
Galvanic Cell (Voltaic cell): It is a device in which a spontaneous chemical reaction generates an electric current i.e., it converts chemical energy into electrical energy. It is commonly known as a battery.
Electrolytic cell: It is a device in which an electric current from an external source drives a non-spontaneous reaction i.e., it converts electrical energy into chemical energy.
Electromotive force: The force that pushes the electrons away from the anode and pulls them towards cathode is called the electromotive force (emf) or the cell potential.
Standard Hydrogen Electrode (SHE): It is used as the reference electrode. It has been assigned an orbitary emf of exactly zero volt. It consists of a platinum electrode in contact with 1M HC1 solution and 1 atm hydrogen gas. The hydrogen gas is bubbled through the solution at 25°C.
Electrode potential (E): Electromotive force of a cell in which the electrode on the left is a standard hydrogen electrode and the electrode on the right is the electrode in question.
Standard electrode potential (E°): The value of the standard emf of a cell in which molecular hydrogen under standard pressure is oxidised to solvated protons at the left hand electrode.
Nernst equation: It is the one which relates the cell potential and the concentration of the species involved in an electrochemical reaction.
Electrolysis: The process of chemical decomposition of an electrolyte in solution or molten state by the passage of electric current is called electrolysis.
Faraday’s first law of electrolysis: The mass of the substance (m) liberated at an electrode during electrolysis is directly proportional to the quantity of charge (Q) passed through the cell.
m ∝ Q (OR) m ∝ It (OR) m = Z It.
Faraday’s second law of electrolysis: When the same quantity of charge is passed through the solutions of different electrolytes, the amount of substances liberated at the respective electrodes are directly proportional to their electrochemical equivalents.
Electrochemical equivalent: It is defined as the amount of substance deposited or liberated at the electrode by a charge of one coulomb (one ampere current passing for one second).
Battery: It is a device that produces electrons through electrochemical reactions, and contains positive and negative terminals. A battery consists of one or more electro chemical cells, which transform stored chemical energy directly into electrical energy.
Fuel cell: The galvanic cell in which the energy of combustion of fuels is directly converted into electrical energy is called the fuel cell.
Corrosion: The spontaneous destruction of metals due to their interaction with environment
is called corrosion.
Protection of metals from corrosion: Following methods helps to protect metals from corrosion,
- Coating metal surface by paint.
- Galvanizing – by coating with another metal such as zinc.
- Cathodic protection
1. Variation of molar conductivity with concentration.
| Concentration (M) | Molar conductance ( x10‘3Sm2 mol-1) | ||
| NaCl | KCl | HCl | |
| 0.1 | 10.674 | 12.896 | 39.132 |
| 0.01 | 11.851 | 14.127 | 41.20 |
| 0.0001 | 12.374 | 14.695 | 42.136 |
2. ∧°m values for various compounds.
| Electrolyte | ∧°m at 298 K | Difference |
| KCl NaCl |
149.86 126.45 |
23.41 |
| KBr NaBr |
151.92 128.51 |
23.41 |
| knO3 NaNO3 |
114.96 121.55 |
23.41 |
| Electrolyte | ∧°m at 298 in K | Difference |
| KBr KCl |
151.92 149.86 |
2.06 |
| NaBr KCl |
128.51 126.45 |
2.06 |
| LiBr LiCl |
117.09 115.03 |
2.06 |