Electrochemistry
Electrochemistry deals with chemical changes involving electricity. Some chemical reactions require electric current and some chemical reactions produce electric current.
Conductors: The substances which allow current to pass through them. Conductors are of two types:
- Electronic conductors: The substances which allow current to pass through them without undergoing any physical or chemical change are called electronic conductors. Examples: metals, gas carbon, petroleum coke, CdS and CuS.
- Electrolytic conductors: Substances which conducts electricity in molten state or in aqueous solution because of some chemical change are called electrolytic conductors or electrolytes. Examples: All salts, acids and bases.
Arrhenius theory of electrolytic dissociation
It explains the behaviour of weak electrolytes. Any electrolyte must ionise and should be in equilibrium with unionised substance.
Electrolysis: The decomposition of a chemical compound in the molten state or in the solution state into its constituent elements under the influence of an applied emf is called electrolysis. It is a redox reaction and endo-energic reaction.
The conductance or the current conducting capacity of an electrolytic solution can be expressed as:
- Specific conductance (k)
- Molar conductance (μ)
- Equivalent conductance (∧)
Effect of Temperature: The conductivity of all electrolytes increases with increase in temperature.
Faradays Laws of Electrolysis
First law: The amount of substance deposited or dissolved or evolved at an electrode in an electrolysis process is directly proportional to the amount of electricity passed through the electrolyte.
Second law: When equal amount of electricity is passed through one or more electrolytes connected in series the weights of different substances deposited or liberated or dissolved at the electrodes are directly proportional to the chemical equivalents of the substances.
Applications of Electrolysis
- To determine the equivalent weights.
- To extract more electropositive metals like Na, K, Mg, Al.
- To extract non-metals like F2, Cl2, H2, O2.
- To obtain compounds like NaOH, Na2CO3.
- In electroplating to prevent corrosion.
Galvanic cells (Voltaic or electrochemical cells): It is a device which makes use of spontaneous redox reaction for the generation of electrical energy.