THE CONCEPT OF ELECTROLYSIS CHARACTERISTICS OF ELECTROCHEMICAL PROCESS

UDC 004
THE CONCEPT OF ELECTROLYSIS CHARACTERISTICS OF ELECTROCHEMICAL
PROCESS
Orynbek A. – students of ХТ-20-14к
Seitmagzimova G. – senior teacher
Electrochemical reaction, any process either caused or accompanied by the passage of
an electric current and involving in most cases the transfer of electrons between two substances—one
a solid and the other a liquid.
Under ordinary conditions, the occurrence of a chemical reaction is accompanied by the
liberation or absorption of heat and not of any other form of energy; but there are many chemical
reactions that—when allowed to proceed in contact with two electronic conductors, separated by
conducting wires—liberate what is called electrical energy, and an electric current is generated.
Conversely, the energy of an electric current can be used to bring about many chemical reactions that
do not occur spontaneously. A process involving the direct conversion of chemical energy when
suitably organized constitutes an electrical cell. A process whereby electrical energy is converted
directly into chemical energy is one of electrolysis; i.e., an electrolytic process. By virtue of their
combined chemical energy, the products of an electrolytic process have a tendency to react
spontaneously with one another, reproducing the substances that were reactants and were therefore
consumed during the electrolysis. If this reverse reaction is allowed to occur under proper conditions,
a large proportion of the electrical energy used in the electrolysis may be regenerated. This possibility
is made use of in accumulators or storage cells, sets of which are known as storage batteries. The
charging of an accumulator is a process of electrolysis; a chemical change is produced by the electric
current passing through it. In the discharge of the cell, the reverse chemical change occurs, the
accumulator acting as a cell that produces an electric current.
Finally, the passage of electricity through gases generally causes chemical changes, and this
kind of reaction forms a separate branch of electrochemistry that will not be treated here.
Substances that are reasonably good conductors of electricity may be divided into two groups:
the metallic, or electronic, conductors and the electrolytic conductors. The metals and many
nonmetallic substances such as graphite, manganese dioxide, and lead sulfide exhibit metallic
conductivity; the passage of an electric current through them produces heating and magnetic effects
but no chemical changes. Electrolytic conductors, or electrolytes, comprise most acids, bases, and
salts, either in the molten condition or in solution in water or other solvents. Plates or rods composed
of a suitable metallic conductor dipping into the fluid electrolyte are employed to conduct the current
into and out of the liquid; i.e., to act as electrodes. When a current is passed between electrodes
through an electrolyte, not only are heating and magnetic effects produced but also definite chemical
changes occur. At or in the neighbourhood of the negative electrode, called the cathode, the chemical
change may be the deposition of a metal or the liberation of hydrogen and formation of a basic
substance or some other chemical reduction process; at the positive electrode, or anode, it may be the
dissolution of the anode itself, the liberation of a nonmetal, the production of oxygen and an acidic
substance, or some other chemical oxidation process.
An electrolyte, prepared either by the melting of a suitable substance or by the dissolving of it
in water or other liquid, owes its characteristic properties to the presence in it of electrically charged
atoms or groups of atoms produced by the spontaneous splitting up or dissociation of the molecules of
the substance. In solutions of the so-called strong electrolytes, most of the original substance, or in
some solutions perhaps all of it, has undergone this process of electrolytic dissociation into charged
particles, or ions. When an electrical potential difference (i.e., a difference in degree of electrification)
is established between electrodes dipping into an electrolyte, positively charged ions move toward the
cathode and ions bearing negative charges move toward the anode. The electric current is carried
through the electrolyte by this migration of the ions. When an ion reaches the electrode of opposite
polarity, its electrical charge is donated to the metal, or an electric charge is received from the metal.
The ion is thereby converted into an ordinary neutral atom or group of atoms. It is this discharge of
ions that gives rise to one of the types of chemical changes occurring at electrodes.
The study of electrochemistry began in the 18th century, bloomed until the early 20th century,
and then faded, owing to an excessive use of thermodynamic principles in analyzing the processes that
take place at points in the system where the various parts form interfaces. Since about 1950
electrochemistry has undergone a change. The study of processes in solutions has been less stressed,
but the study of the transfer of electrons between metals and solution has increased explosively. With
this new emphasis electrochemistry is becoming a core science. It promises to be an important part of
the foundation of the ecology-oriented society of the future, because electricity is not a pollutant. The
pollution associated with some methods of generating electricity must, however, be reduced.
Alkali metal hydroxides are manufactured in the United States to the extent of approximately
36,500 tons/day, almost entirely by the electrolysis of aqueous brine solutions. In addition to sodium
hydroxide the electrochemical synthesis results in the co-production of chlorine.
Unlike alkali metal hydroxides, chlorine produced at the anode of an electrolytic cell in
stoichiometric quantities to sodium hydroxide has experienced a declining market because of
environmental problems. For example, use of chlorine by the pulp and paper industry has been
declining because of traces of dioxin formed in paper products; chlorine in the treatment of sewage
and water has been shown to lead to the production of toxic organo-chlorine compounds; compounds
like the chlorofluorocarbons and methyl chloroform have been found to be destructive to the earth's
protective ozone layer, and certain chlorine-containing pesticides have been shown to be toxic to
biological systems. Consequently, it is expected that the declining demand for chlorine will continue
to weaken in the approaching decades. By contrast, the demand for alkali metal hydroxides, like
caustic soda is expected to remain strong.
Accordingly, in view of the declining demand for chlorine and the absence of economical
routes for its destruction or safe storage there is a growing need for new and more economical
processes for the manufacture of high purity alkali metal hydroxides which do not also produce
halogens.
A number of methods have been developed for the production of alkali metal hydroxides
without the simultaneous production of chlorine. While most methods are effective in eliminating the
problems associated with the co-production of chlorine most have not been viewed as commercially
acceptable because of various shortcomings, e.g. inefficient consumption of power, inability to
produce a sufficiently pure grade of caustic soda and/or co- production of other less desirable
products.
The lime-soda process has several shortcomings. It is difficult to carry out to full conversion;
the caustic soda is impure and the process is energy inefficient, particularly if there is any attempt to
recycle the calcium by thermal decomposition of the carbonate to oxide.
References:
1. Oesper, Ralph; Speter, Max (1937). "The Faraday-Whewell correspondence concerning electro-chemical
terms". The Scientific Monthly. 45 (6): 535–546.
2. ^ Fabbri, Emiliana; Schmidt, Thomas J. (5 October 2018). "Oxygen Evolution Reaction—The Enigma in
Water Electrolysis". ACS Catalysis. 8 (10): 9765–9774. doi:10.1021/acscatal.8b02712.
3. ^ Ashworth, William (20 March 2015). "Martinus van Marum - Scientist of the Day". Linda Hall Library.
4. ^ Ihde, Aaron J. (1964). The Development of Modern Chemistry. Harper & Row. pp. 125–127.
5. ^ Jump up to:a b "The History of Electrochemistry: From Volta to Edison". ECS. Retrieved 11 October 2019.
6. ^ Thorpe, Thomas (1896). Humphry Davy, Poet and Philosopher. New York: Macmillan & Co., Limited.