Electrochemistry - is the branch of science which deals with the relationship between electrical energy and chemical changes taking place in red ox reactions that means how chemical energy produced in redox reaction can we convert it into electrical energy or how electrical energy can be used to bring about a redox reaction which is otherwise non spontaneous
another word electrochemistry is a study of production of electricity from the energy released during a spontaneous chemical reaction and the use of electrical energy to bring about non spontaneous chemical transformation.
Some important concepts are briefly reviewed about redox reaction
redox reaction- is the reaction which involved both reduction and oxidation
Oxidation reaction- is a reaction which involved loss of electron while reduction is a reaction which involves gain of electrons in term of electronic concept.
For example
Zn(s) + CuSO4(Aq) ------------> ZnSO4 (aq) + Cu(s)
Or Zn + Cu+2 ----------------> Zn+2 + Cu …........(1)
(Here Zn losses its electron, so, it is oxidized into Zn+2 take place i.e. oxidation take place. while Cu+2 gains electron, therefore, Cu+2 is reduced into Cu i.e. reduction take place.)
Oxidizing agent or oxidant- the substance which gains electron or gets reduced but oxidizes the other substance.
Reducing agent or reductant- the substance which losses electron or get oxidized but reduces the other substance.
A redox reaction may be considered to be made up two half reactions, one involving oxidation and other involving reduction these are called oxidation half reaction and reduction half reaction.
Above reaction (1) may be split into
- Zn -----------------> Zn+2 + 2e- ( oxidation half reaction)
- Cu+2 + 2e- ----------------> Cu (reduction half reaction)
Electrochemical cell
- is a device which is capable of either generating electrical energy from chemical reaction or using electrical energy to cause chemical reaction.
There are two types of electrochemical cell.
1. Galvanic cell or voltaic cell
2. Electrolytic cell
Differences between galvanic and electrolytic cell
s.no.
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features
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Galvanic cell
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electrolytic cell
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1
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definition
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The device which converts the chemical energy of spontaneous redox reaction into electrical energy
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The Device which convert electrical energy into chemical energy
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2
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Nature of redox reaction
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spontaneous
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non spontaneous and take place only when electrical energy is applied
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3
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salt bridge required-
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required to separates two different electrodes kept in different electrolytic solution
example- primary cell and secondary cell |
not required any salt bridge since only one electrolyte is taken
Example- this device is useful for galvanization electroplating and hydrolysis etc |
Salt bridge - is t U-shaped tube containing semi solid paste of inert electrolyte either KCl, KNO3 or ammonium chloride in Agar Agar or gelatin.
Function of salt bridge -
I) to complete the electrical circuit by allowing the ions to flow from one solution to other without mixing of the two solution
II) to maintain the electrical neutrality of the solution in the two half cell (in voltaic cell)