basic concepts of electrochemistry
Electrochemistry:
a science that studies the relationship between electric and chemical phenomena and the conversion disciplines between electric and chemical energy
Differences between the ordinary oxidation-reduction reaction (redox reaction) occurring in solution and in the electrochemical cell.
2Fe3+ + Sn2+ 2Fe2+ + Sn4+
To harvest useful energy, the oxidizing and reducing agent has to be separated physically in two different compartments so as to make the electron passing through an external circuit
Reaction takes place at
electrode/solution interface
half-reactions:
oxidation / anode reaction:
Sn2+ - 2e- Sn4+
reduction / cathode reaction:
2Fe3+ + 2e- 2Fe2+
Electrochemical apparatus:
chemical electric:
primary cell (Galvanic cell)
electric chemical:
electrolytic cell
Electrode: anode, cathode positive electrode; negative electrode
Nomenclature• “Redox” Chemistry: Reduction and Oxidation
• Oxidation: Loss of electrons
• Reduction: Gain of electrons (a reduction in oxidation number)
LEO goes GER
Loss of Electrons is Oxidation
Gain of Electrons is Reduction
Reduction form – electrons = oxidized form
The sum of two half – reactions constitutes the redox reaction, e.g. the oxidation of ferrous ion by ceric ion:
Fe2+ – e = Fe3+ (oxidation half – reaction)Ce4+ + e = Ce3+ (reduction half – reaction)Adding Fe2+ + Ce4+ = Fe3+ + Ce3+ (redox reaction)
Introduction
• Oxidation-reduction reactions are also known as redox reactions
• Def: Redox reactions describe all chemical reactions in which there is a net change in atomic charge
• It is a class of reactions that include:–formation of a compound from its elements–all combustion reactions–reactions that generate electricity–reactions that produce cellular energy
Galvanic Cells (cont.)• In turns out that we still will not get electron flow
in the example cell. This is because charge build-up results in truncation of the electron flow.
• We need to “complete the circuit” by allowing positive ions to flow as well.
• We do this using a “salt bridge” which will allow charge neutrality in each cell to be maintained.
Galvanic Cells (cont.)
Salt bridge/porous disk: allows for ion migration suchthat the solutions will remain neutral.
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