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Sablon:Longintro Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics and chemical equilibrium.

Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a macroscopic or supra-molecular science, as the majority of the principles on which it was founded relate to the bulk rather than the molecular/atomic structure alone (for example, chemical equilibrium and colloids).

Some of the relationships that physical chemistry strives to resolve include the effects of:

  1. Intermolecular forces that act upon the physical properties of materials (plasticity, tensile strength, surface tension in liquids).
  2. Reaction kinetics on the rate of a reaction.
  3. The identity of ions and the electrical conductivity of materials.
  4. Surface science and electrochemistry of cell membranes.[1]
  5. Interaction of one body with another in terms of quantities of heat and work called thermodynamics.
  6. Transfer of heat between a chemical system and its surroundings during change of phase or chemical reaction taking place called thermochemistry
  7. Study of colligative properties of number of species present in solution.
  8. Number of phases, number of components and degree of freedom (or variance) can be correlated with one another with help of phase rule.
  9. Reactions of electrochemical cells.

Key concepts[szerkesztés]

The key concepts of physical chemistry are the ways in which pure physics is applied to chemical problems.

One of the key concepts in classical chemistry is that all chemical compounds can be described as groups of atoms bonded together and chemical reactions can be described as the making and breaking of those bonds. Predicting the properties of chemical compounds from a description of atoms and how they bond is one of the major goals of physical chemistry. To describe the atoms and bonds precisely, it is necessary to know both where the nuclei of the atoms are, and how electrons are distributed around them.[2]
Quantum chemistry, a subfield of physical chemistry especially concerned with the application of quantum mechanics to chemical problems, provides tools to determine how strong and what shape bonds are,[2] how nuclei move, and how light can be absorbed or emitted by a chemical compound.[3] Spectroscopy is the related sub-discipline of physical chemistry which is specifically concerned with the interaction of electromagnetic radiation with matter.

Another set of important questions in chemistry concerns what kind of reactions can happen spontaneously and which properties are possible for a given chemical mixture. This is studied in chemical thermodynamics, which sets limits on quantities like how far a reaction can proceed, or how much energy can be converted into work in an internal combustion engine, and which provides links between properties like the thermal expansion coefficient and rate of change of entropy with pressure for a gas or a liquid.[4] It can frequently be used to assess whether a reactor or engine design is feasible, or to check the validity of experimental data. To a limited extent, quasi-equilibrium and non-equilibrium thermodynamics can describe irreversible changes.[5] However, classical thermodynamics is mostly concerned with systems in equilibrium and reversible changes and not what actually does happen, or how fast, away from equilibrium.

Which reactions do occur and how fast is the subject of chemical kinetics, another branch of physical chemistry. A key idea in chemical kinetics is that for reactants to react and form products, most chemical species must go through transition states which are higher in energy than either the reactants or the products and serve as a barrier to reaction.[6] In general, the higher the barrier, the slower the reaction. A second is that most chemical reactions occur as a sequence of elementary reactions,[7] each with its own transition state. Key questions in kinetics include how the rate of reaction depends on temperature and on the concentrations of reactants and catalysts in the reaction mixture, as well as how catalysts and reaction conditions can be engineered to optimize the reaction rate.

The fact that how fast reactions occur can often be specified with just a few concentrations and a temperature, instead of needing to know all the positions and speeds of every molecule in a mixture, is a special case of another key concept in physical chemistry, which is that to the extent an engineer needs to know, everything going on in a mixture of very large numbers (perhaps of the order of the Avogadro constant, 6 x 1023) of particles can often be described by just a few variables like pressure, temperature, and concentration. The precise reasons for this are described in statistical mechanics,[8] a specialty within physical chemistry which is also shared with physics. Statistical mechanics also provides ways to predict the properties we see in everyday life from molecular properties without relying on empirical correlations based on chemical similarities.[5]

History[szerkesztés]

Lásd még: History of chemistry
Fragment of M. Lomonosov's manuscript 'Physical Chemistry' (1752)

The term "physical chemistry" was coined by Mikhail Lomonosov in 1752, when he presented a lecture course entitled "A Course in True Physical Chemistry" (Russian: «Курс истинной физической химии») before the students of Petersburg University.[9] In the preamble to these lectures he gives the definition: "Physical chemistry is the science that must explain under provisions of physical experiments the reason for what is happening in complex bodies through chemical operations".

Modern physical chemistry originated in the 1860s to 1880s with work on chemical thermodynamics, electrolytes in solutions, chemical kinetics and other subjects. One milestone was the publication in 1876 by Josiah Willard Gibbs of his paper, On the Equilibrium of Heterogeneous Substances. This paper introduced several of the cornerstones of physical chemistry, such as Gibbs energy, chemical potentials, and Gibbs' phase rule.[10] Other milestones include the subsequent naming and accreditation of enthalpy to Heike Kamerlingh Onnes and to macromolecular processes. [forrás?]

The first scientific journal specifically in the field of physical chemistry was the German journal, Zeitschrift für Physikalische Chemie, founded in 1887 by Wilhelm Ostwald and Jacobus Henricus van 't Hoff. Together with Svante August Arrhenius,[11] these were the leading figures in physical chemistry in the late 19th century and early 20th century. All three were awarded the Nobel Prize in Chemistry between 1901–1909.

Developments in the following decades include the application of statistical mechanics to chemical systems and work on colloids and surface chemistry, where Irving Langmuir made many contributions. Another important step was the development of quantum mechanics into quantum chemistry from the 1930s, where Linus Pauling was one of the leading names. Theoretical developments have gone hand in hand with developments in experimental methods, where the use of different forms of spectroscopy, such as infrared spectroscopy, microwave spectroscopy, electron paramagnetic resonance and nuclear magnetic resonance spectroscopy, is probably the most important 20th century development.

Further development in physical chemistry may be attributed to discoveries in nuclear chemistry, especially in isotope separation (before and during World War II), more recent discoveries in astrochemistry,[12] as well as the development of calculation algorithms in the field of "additive physicochemical properties" (practically all physicochemical properties, such as boiling point, critical point, surface tension, vapor pressure, etc.—more than 20 in all—can be precisely calculated from chemical structure alone, even if the chemical molecule remains unsynthesized),[forrás?] and herein lies the practical importance of contemporary physical chemistry.

See Group contribution method, Lydersen method, Joback method, Benson group increment theory, quantitative structure–activity relationship


Die physikalische Chemie (kurz: PC oder Phys.Chem., auch: Physikochemie) ist neben der anorganischen und der organischen Chemie eines der „klassischen“ Teilgebiete der Chemie. Sie behandelt den Grenzbereich zwischen Physik und Chemie, insbesondere die Anwendung von Methoden der Physik auf Objekte der Chemie, weshalb manchmal auch der Begriff chemische Physik verwendet wird. Während in der präparativen Chemie Fragestellungen der Methodik der chemischen Synthese bekannter und neuer Substanzen im Vordergrund stehen, versucht die physikalische Chemie mit Hilfe theoretischer und experimenteller Methoden die Eigenschaften von Stoffen und deren Umwandlung zu beschreiben, mit dem Ziel, für alle relevanten Vorgänge allgemein gültige mathematische Formeln mit klar definierten Einheiten und exakten Zahlenwerten aufzustellen.

Naturgemäß besteht eine große Nähe zur Physik (insbesondere zur Molekülphysik), und die Klassifikation eines Forschungsthemas als „Physik“ oder „Chemie“ ist häufig wenig eindeutig. Trotzdem wird teilweise je nach Schwerpunktsetzung zwischen physikalischer Chemie und chemischer Physik unterschieden. Die physikalische Chemie liefert die theoretischen Grundlagen für die Technische Chemie und die Verfahrenstechnik. Chemiker, die vorwiegend im Bereich der physikalischen Chemie tätig sind, werden als Physikochemiker bezeichnet. Die physikalische Chemie gehört zum Pflichtteil in jedem Chemiestudium.

Geschichte[szerkesztés]

mini|Svante Arrhenius (1909) Die ersten Lehrgänge zu Themen aus der physikalischen Chemie wurden um 1752 an der Lomonossow-Universität in Moskau von Michail Lomonossow gehalten. 1890 führten Svante Arrhenius, Jacobus Henricus van ’t Hoff, Wilhelm Ostwald und Walther Nernst erstmals die physikalische Chemie als eigenständiges Lehrfach an Hochschulen ein. Als Begründer der physikalischen Chemie im angelsächsischen Raum gilt Josiah Willard Gibbs mit seinem 1867 veröffentlichten Artikel „On the Equilibrium of Heterogeneous Substances“, in dem er die grundlegenden Konzepte Freie Energie, chemisches Potential und Phasenregel entwickelte. Die Arbeiten von Gibbs, Robert Mayer, Hermann Helmholtz, Jacobus Henricus van ’t Hoff bildeten für Wilhelm Ostwald eine wichtige Verkettung des Energiebegriffes aus chemischer Sicht.

Gustav Wiedemann erhielt 1871 in Leipzig den ersten deutschen Lehrstuhl für physikalische Chemie.[13] Erst 1887 konnte sich nach Neubesetzung des Lehrstuhls mit Wilhelm Ostwald die physikalische Chemie in der Forschung manifestieren. Ostwald wurde erster Herausgeber der 1887 gemeinsam mit van ’t Hoff gegründeten Zeitschrift für physikalische Chemie, Stöchiometrie und Verwandtschaftslehre.

Weitere spezifisch der physikalischen Chemie gewidmete Institute folgten dann auf Anregung seines Schülers Walther Nernst in rascher Folge in Göttingen (1891)[14], Dresden (1900)[15], Karlsruhe (1900)[16], Berlin (1905)[17], Aachen (1906)[18], Breslau (1910)[19] und andernorts.[20]

Wilhelm Ostwald gründete 1894 die Deutsche Elektrochemische Gesellschaft, die 1901 in Deutsche Bunsen-Gesellschaft für Angewandte Physikalische Chemie umbenannt wurde. In England wurde 1903 die Faraday Society (heute Faraday Division der Royal Society of Chemistry) gegründet. Inzwischen beschäftigen sich unzählige Universitäts- und mehrere Max-Planck-Institute mit physikalischer Chemie.

Einen detaillierten Überblick über die Entstehung und Entwicklung der Physikalischen Chemie gibt ein Übersichtsartikel der Bunsen-Gesellschaft.[21] Weitere Details finden sich unter Geschichte der Chemie, eine Liste bedeutender Physikochemiker an allen deutschen Universitäten[22] befindet sich hier.[23]

  1. ↑ Torben Smith Sørensen. Surface chemistry and electrochemistry of membranes. CRC Press, 134. o. (1999). ISBN 0-8247-1922-0 
  2. ↑ a b Atkins, Peter and Friedman, Ronald (2005). Molecular Quantum Mechanics, p. 249. Oxford University Press, New York. ISBN 0-19-927498-3.
  3. ↑ Atkins, Peter and Friedman, Ronald (2005). Molecular Quantum Mechanics, p. 342. Oxford University Press, New York. ISBN 0-19-927498-3.
  4. ↑ Landau, L. D. and Lifshitz, E. M. (1980). Statistical Physics, 3rd Ed. p. 52. Elsevier Butterworth Heinemann, New York. ISBN 0-7506-3372-7.
  5. ↑ a b Hill, Terrell L. (1986). Introduction to Statistical Thermodynamics, p. 1. Dover Publications, New York. ISBN 0-486-65242-4.
  6. ↑ Schmidt, Lanny D. (2005). The Engineering of Chemical Reactions, 2nd Ed. p. 30. Oxford University Press, New York. ISBN 0-19-516925-5.
  7. ↑ Schmidt, Lanny D. (2005). The Engineering of Chemical Reactions, 2nd Ed. p. 25, 32. Oxford University Press, New York. ISBN 0-19-516925-5.
  8. ↑ Chandler, David (1987). Introduction to Modern Statistical Mechanics, p. 54. Oxford University Press, New York. ISBN 978-0-19-504277-1.
  9. ↑ Alexander Vucinich. Science in Russian culture. Stanford University Press, 388. o. (1963). ISBN 0-8047-0738-3 
  10. ↑ Josiah Willard Gibbs, 1876, "On the Equilibrium of Heterogeneous Substances", Transactions of the Connecticut Academy of Sciences
  11. ↑ Laidler, Keith. The World of Physical Chemistry. Oxford: Oxford University Press, 48. o. (1993). ISBN 0-19-855919-4 
  12. ↑ Herbst, Eric (2005. május 12.). „Chemistry of Star-Forming Regions”. Journal of Physical Chemistry A 109, 4017–4029. o. DOI:10.1021/jp050461c. PMID 16833724.  
  13. ↑ Uni Leipzig Physikalische Chemie, 1887 im „Zweiten Chemischen Institut“, Brüderstr. 34, und 1898 im neuen „Ostwald Institut für Physikalische und Theoretische Chemie“, Linnestr. 2
  14. ↑ Uni Göttingen 1891 im Physikalischen Institut, Michaelishaus am Leinekanal, und 1896 als neues „Inst. für Physikal. Chemie“
  15. ↑ TH Dresden 1900 als „Elektrochemisches Laboratorium“
  16. ↑ TH Karlsruhe 1900 als „Inst. für Physikal. Chemie“
  17. ↑ Uni Berlin im II. Chemisches Institut (siehe unter „Geschichte“), 1905 als „Physikalisch-Chemisches Institut“
  18. ↑ TH Aachen 1897 als „Elektrochemie“, 1906 mit Lehrstuhl als „Theoretische Hüttenkunde und Physikalische Chemie“
  19. ↑ TH Breslau 1910 als „Inst. für physikal. Chemie“; Sablon:NDB
  20. ↑ 100 Jahre Physikalische Chemie in Aachen[halott link] (PDF; 1,9 MB); 100 Jahre Physikalische Chemie in Karlsruhe (PDF; 109 kB)
  21. ↑ Manfred Zeidler 100 Jahre Physikalische Chemie an der RWTH Aachen, S. 91[halott link] (PDF; 1,9 MB)
  22. ↑ Institute für physikalische Chemie in Deutschland und Österreich
  23. ↑ Übersicht aller Lehrstühle und Abteilungen für physikalische Chemie[halott link] (PDF; 9 MB)
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