physical chemistry

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physical chemistry,

branch of sciencescience
[Lat. scientia=knowledge]. For many the term science refers to the organized body of knowledge concerning the physical world, both animate and inanimate, but a proper definition would also have to include the attitudes and methods through which this body of
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 that combines the principles and methods of physics and chemistry. It provides a fundamental theoretical and experimental basis for all of chemistry, including organic, inorganic, and analytical chemistry. In addition, it is the foundation of chemical engineering. Topics of interest are chemical equilibrium, reaction rates, solutions, molecular weights, molecular structure, and the properties of gases, liquids, crystals, and colloids. Among other factors, the influence of temperature, pressure, electricity, light, concentration, and turbulence are considered. There are three principal approaches in physical chemistry: thermodynamicsthermodynamics,
branch of science concerned with the nature of heat and its conversion to mechanical, electric, and chemical energy. Historically, it grew out of efforts to construct more efficient heat engines—devices for extracting useful work from expanding hot gases.
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, involving large numbers of molecules in equilibrium; kinetics, involving chemical changes with time; and molecular structure, involving the electronic and atomic arrangements that follow from the quantum theoryquantum theory,
modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity together form the theoretical basis of modern physics.
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. The latter approach is primarily theoretical and provides an understanding of the chemical bondschemical bond,
mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as an
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 which are responsible for the structure of all materials.

Bibliography

See I. N. Levine, Physical Chemistry (4th ed. 1995); G. M. Barrow, Physical Chemistry (6th ed. 1996); P. W. Atkins, Physical Chemistry (6th ed. 1997); D. A. McQuarrie and J. D. Simon, Physical Chemistry: A Molecular Approach (1997).

Physical Chemistry

 

the science that seeks to elucidate chemical phenomena and determine the laws governing the phenomena on the basis of the general principles of physics. The main divisions of physical chemistry are chemical thermodynamics, chemical kinetics, the study of catalysis, of surface phenomena, and of solutions, quantum chemistry, and the study of the structure and properties of molecules, ions, and radicals. By virtue of its largely independent divisions, physical chemistry also includes colloid chemistry, electrochemistry, photochemistry, crystal chemistry, radiochemistry, and physicochemical analysis.

The name and the subject matter of physical chemistry were first set forth by M. V. Lomonosov, who in 1752 and 1753 gave a course entitled “Introduction to True Physical Chemistry.” Lomonosov established one of the fundamental laws of physical chemistry—the law of the conservation of mass in chemical reactions. In 1840, G. I. Gess (G. H. Hess) discovered the law of constant heat summation in chemical reactions, which also proved to be one of the basic laws of physical chemistry. A significant contribution to the development of physical chemistry in the mid–19th century was made by P. Berthelot and J. Thomsen through their basic research in thermochemistry, their introduction of the concept of heats of reaction as a measure of the chemical affinity of reactants, and their establishment of the relationship between heats of formation and the composition of substances. The first chair of physical chemistry was founded in 1887 at the University of Leipzig by W. Ostwald, who also founded the first journal of physical chemistry.

Physical chemistry emerged as an independent branch of science only toward the end of the 19th century. Its evolution was spurred by the upsurge in chemical production and the creation of chemical industries. Empirical rules and qualitative relationships were insufficient for the problems posed by industry.

The development of physical chemistry in the second half of the 19th and early 20th centuries was characterized by the application of mainly thermodynamic methods, the study of macroscopic, that is, directly observable, characteristics of systems and processes, and the use of classical physics and the classical theory of chemical structure in studying the relationship between the properties and structure of molecules. The equation of state for ideal gases was definitively established (D. I. Mendeleev, B. Clapeyron). Research was done on the application of thermodynamics to chemical and phase equilibria (J. Gibbs, J. van’t Hoff, W. Nernst, H. Le Châtelier, N. S. Kurnakov, G. Tammann); the principles of macroscopic (assuming ideal substances) kinetics were developed (C. Guldberg, P. Waage, N. N. Beketov, van’t Hoff); and the concept of the energy of activation of reactions was introduced (S. Arrhenius). Advances were made in catalysis on the basis of the principles set forth by M. Faraday, and the fundamental laws of adsorption were established (Gibbs). The thermodynamic theory of dilute solutions was developed (F. Raoult, van’t Hoff, D. P. Konovalov); the theory of electrolytic dissociation was formulated (Arrhenius); and the concept of electrode potentials for galvanic cells was introduced (Nernst).

The results of the research carried out during this stage in the development of physical chemistry were implemented in industry in, for example, the synthesis of ammonia and the exploitation of salt deposits, in certain metallurgical processes, and in distillation and rectification.

Such important achievements in science in the late 19th and early 20th centuries as the discovery of X rays, the electron, and radioactivity and the development of spectroscopy provided the background for a new stage in physical chemistry. The establishment of the laws governing the motion of electrons in atoms and molecules (laws of quantum mechanics) led to the emergence of quantum chemistry, which made possible new theoretical interpretations of chemical bonds, valence, and chemical structure.

The principal features of modern physical chemistry, which is taken to begin in the 1920’s, are the widespread use of various physical methods of experimental research and the attempt to elucidate the detailed molecular mechanism of chemical reactions. Physical chemistry provides the theoretical basis for research in inorganic, organic, and analytical chemistry; its findings are also used in chemical technology. The period from the 1950’s through the 1970’s witnessed a rapid development of many areas of physical chemistry and the emergence of new trends associated with the detailed study of molecules, atoms, and radicals in various chemical and physical processes, including those occurring under the effect of gamma radiation, high-energy particle fluxes, and laser radiation. Research is being done on the energies of dissociation, ionization, and photo-ionization. Reactions occurring in electrical discharges have been profitably studied, as have processes in low-temperature plasma (plasma chemistry) and the effects of surface phenomena on the properties of solids (physicochemical mechanics). Advances are being made in the physical chemistry of polymers and in the electrochemistry of gases.

Scientific institutions. In the USSR, research in physical chemistry is being conducted by the Academy of Sciences of the USSR at the Institute of Physical Chemistry, the N. S. Kurnakov Institute of General and Inorganic Chemistry, the Institute of Chemical Physics, the Institute of Electrochemistry, the Institute of Chemistry (Gorky), and the Institute of New Problems in Chemistry (Chernogolovka, Moscow Oblast).

Research is also carried out by the institutes of the Far East and the Ural scientific centers of the Academy of Sciences of the USSR and the institutes of the academy’s Kazan and Kola branches. Included here are the Institute of Chemistry (Vladivostok), the Institute of Electrochemistry (Sverdlovsk), and the A. E. Arbuzov Institute of Organic and Physical Chemistry (Kazan). The institutes of the Siberian Division of the Academy of Sciences of the USSR involved in research in physical chemistry include the Institute of Catalysis, the Institute of Chemical Kinetics and Combustion, and the Institute of Physicochemical Principles for the Processing of Inorganic Raw Materials. Research in physical chemistry is also being conducted in nearly all chemical institutes of the academies of sciences of the Union republics, as well as in more than 150 research institutes and institute branches linked to various sectors of the economy, for example, the L. la. Karpov Physical Chemistry Institute. Advanced research in physical chemistry is also being conducted at institutes and universities in other countries.

REFERENCES

Glasstone, S. Teoreticheskaia khimiia. Moscow, 1950. (Translated from English.)
Moelwyn-Hughes, E. A. Fizicheskaia khimiia, books 1–2. Moscow 1962. (Translated from English.)
Kurs fizicheskoi khimii, 2nd ed., vols. 1–2. Moscow, 1969–73.
Solov’ev, Iu. I. Ocherkipo istorii fizicheskoi khimii. Moscow, 1964.

physical chemistry

[′fiz·ə·kəl ′kem·ə·strē]
(chemistry)
The branch of chemistry that deals with the interpretation of chemical phenomena and properties in terms of the underlying physical processes, and with the development of techniques for their investigation.
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