Chemistry - Electrochemistry
The combustion of methane is a redox reaction and can be described by the
Adding these half-equations together gives the redox equation for the
combustion of methane.
When the reductant CH4 combines directly with the oxidant O2, chemical
energy is converted into thermal energy.
However, if the reductant (and the site of oxidation) is kept separate
from the oxidant (and the site of reduction), the movement of electrons
from the site of oxidation to the site of reduction during a redox reaction
becomes a source of electrical energy, i.e. electricity.
Electrochemistry involves the study of chemical reactions in which either
chemical energy is converted to electrical energy or electrical energy is
converted to chemical energy.
In electrochemical cells, it is possible to generate an electric current
from a spontaneous chemical reaction or use electrical energy to bring
about a non-spontaneous chemical reaction.
In galvanic cells, chemical energy is converted to electrical energy.
In electrolytic cells, electrical energy is converted to chemical energy.
The effective functioning of all electrochemical cells requires both
electronic conduction and electrolytic conduction.
Electronic conduction involves the movement of electrons in a metal or
Electrolytic conduction involves the movement of cations (positive) and
anions (negative) in opposite directions in a conducting liquid, e.g.
molten ionic compounds such as NaCl(l) or aqueous solutions of ionic or
polar covalent substances such as KCl(aq) or HCl(aq).
Electronic conduction occurs in the external circuit, which includes the
device to be powered (galvanic cell) or the power source (electrolytic
cell). Electrolytic conduction occurs in the internal circuit. In all redox
reactions, and hence all electrochemical cells, electrons move from the
reductant (site of oxidation) to the oxidant (site of reduction).
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