physical chemistry

Scientific analysis of the properties and behavior of chemical systems primarily by physical theory and technique, as, for example, the thermodynamic analysis of macroscopic chemical phenomena.

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. The term chemical physics is often employed to denote a branch of physical chemistry where the emphasis is on the interpretation and analysis of the physical properties of individual molecules and bulk systems, instead of their reactions. Theoretical chemistry is another major branch, where the emphasis is on the calculation of the properties of molecules and systems, and which used the techniques of quantum mechanics and statistical thermodynamics. It is convenient to regard physical chemistry as dealing with three aspects of matter: its equilibrium properties, structure, and ability to change.

Equilibrium properties

The study of matter in a state of equilibrium constitutes the field of chemical thermodynamics. In particular, chemical thermodynamics provides a technique for discussing the response of a system to a change in the external conditions (such as the shift in the boiling and freezing point of either a pure substance or a mixture when the applied pressure is changed, or when the composition of the mixture is modified), and for rationalizing the energy changes that occur in the course of a chemical reaction. The branch of thermodynamics dealing with the latter is called thermochemistry. Chemical thermodynamics also provides a framework for the determination of the maximum amount of work that may be generated by a system undergoing a specified change, and it therefore provides a way of establishing bounds for the efficiencies of a variety of devices, including engines, refrigerators, and electrochemical cells. Thermodynamics is used in chemistry to assess the position of equilibrium of a chemical reaction (that is, how far it will proceed), and to determine what conditions are necessary in order to optimize the yield of a particular product. The branch of chemical thermodynamics dealing with ionic reactions occurring in the presence of electrodes constitutes the field of equilibrium electrochemistry. See also Chemical equilibrium; Chemical thermodynamics; Electrochemistry; Enthalpy; Entropy; Free energy.

Structure

The principal role of quantum mechanics in chemistry is in the discussion of atomic and molecular structure, and in the interpretation of spectroscopic data. In the branch of physical chemistry known as computational quantum chemistry, interest centers on the numerical solution of the Schrödinger equation in order to obtain wave functions and geometries of molecules. Computational quantum chemistry is so developed that it is capable of being used to map the changes in the structures of molecules while they are in the course of reaction, when atoms and groups of atoms are being transferred from one molecule to another. See also Quantum chemistry.

Spectroscopic techniques are used not only to identify molecules present in a sample, but also to determine their shape, size, and electron distribution. The techniques fall into four categories: absorption spectroscopy, emission spectroscopy, Raman spectroscopy, and resonance techniques. See also Electron paramagnetic resonance (EPR) spectroscopy; Electron spectroscopy; Molecular structure and spectra; Mössbauer effect; Nuclear magnetic resonance (NMR); Photochemistry; Spectroscopy.

Techniques for the investigation of molecular structure based on diffraction depend on the observation of the direction through which radiation and particles are scattered when they impinge on a sample. Other techniques for investigating structure include the electric and magnetic properties of molecules, in particular, the determination of electric polarizabilities and dipole moments, magnetic properties, and the properties based on optical birefringence, such as optical activity and the Faraday effect.

Structural properties and thermodynamic properties are brought together by statistical thermodynamics. This major theoretical procedure gives a way of predicting the thermodynamic properties of assemblies of molecules in terms of their individual energy levels.

Physical and chemical change

The third major branch of physical chemistry is concerned with change: physical change and chemical change. In particular, it is concerned with the rate of change. Physical change includes the diffusion of one substance into another, or the migration of ions in an electrode solution. The application of thermodynamics to change in general constitutes the field of nonequilibrium thermodynamics. See also Gas; Transport processes.

Chemical change may be studied at a variety of levels. Empirical chemical kinetics is the study of reactions in order to determine how their rates depend on the concentrations of the participants in the reaction and on the conditions, mainly the temperature. Investigation of the time dependence of reactions yields a detailed picture of the sequence of molecular transformations involved in a complex chemical reaction. See also Chemical dynamics; Shock tube; Ultrafast molecular processes.

An important extension of chemical kinetics is to the reactions that occur on surfaces; these are the processes involved in heterogeneous catalysis. A special application of surface chemistry is to the stability of colloidal suspensions of species in fluids, and another is to the processes that occur at the interface between an electrode and the solution in which it is immersed. See also Adsorption; Colloid; Heterogeneous catalysis.

For more information on physical chemistry, visit Britannica.com.

Physical chemistry (also called physicochemistry) is the application of physics to macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems^[1] within the field of chemistry traditionally using the principles, practices and concepts of thermodynamics, quantum chemistry, statistical mechanics and kinetics.^[2] It is mostly defined as a large field of chemistry, in which several sub-concepts are applied; the inclusion of quantum mechanics is used to illustrate the application of physical chemistry to atomic and particulate chemical interaction or experimentation.^[1]

Physical chemistry is mostly referred to as a macromolecular doctrine, as the majority of the principles on which physical chemistry was founded are composed entirely of macromolecular concepts, such as colloids.^{[3][dubious – discuss]}

The relationships that physical chemistry tries to resolve include the effects of:

1. Intermolecular forces on 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 on the electrical conductivity of materials.

Contents 1 History 2 Notes 3 References 4 See also 4.1 Sub-topics 4.2 Publications

History

The term "physical chemistry" was probably first introduced 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.

The foundation of modern physical chemistry is thought to have been laid in the 1860s to 1880s by 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, which contained several of the cornerstones of physical chemistry, such as Gibbs energy, chemical potentials, Gibbs phase rule ^[4] and subsequent naming and accreditation of enthalpy to Heike Kamerlingh Onnes and to macromolecular processes.^{[citation needed]}

The first scientific journal for publications 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, which were two of the other leading figures of physical chemistry in the late 19th century and early 20th century together with Svante August Arrhenius. All three were awarded with the Nobel Prize in Chemistry in the period 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, EPR spectroscopy and NMR spectroscopy, is probably the most important 20th century development.

Notes

1. ^ ^{a b} Physical Chemistry (p3 - "PHYSICAL CHEMISTRY"), states that the field of physical chemistry is concerned with the microscopic and the macroscopic phenomenon which are mostly concerned with thermodynamics, and kinetics; the field of atomic and particulate interaction being included is implied with the inclusion of quantum chemistry.
2. ^ Quantum Chemistry (p3 - "PHYSICAL CHEMISTRY"), states that "We can divide physical chemistry into four areas: thermodynamics, quantum chemistry, statistical mechanics and kinetics".
3. ^ Physical Chemistry of Macromolecules (p1 - "INTRODUCTION"), defines the formation of physical chemistry as being between macromolecules and colloids in modern physical chemistry. Also defines the "fierce battles" in the 1900s between the inclusion of colloids AS macromolecules.
4. ^ Josiah Willard Gibbs, 1876, "On the Equilibrium of Heterogeneous Substances", Transactions of the Connecticut Academy of Sciences

References

1. Levine, I. N. (1978). Physical Chemistry McGraw-Hill publishing ISBN 0-07-037418-X
2. Atkins, P.W. (1978). Physical Chemistry Oxford University Press ISBN 0-7167-3539-X
3. Berry, S. R., Rice, S. A, Ross, J. (2000). Physical Chemistry 2nd ed. Oxford University Press. ISBN 0-19-510589-3
4. Hunter, R. J. (1993) Introduction to Modern Colloid Science Oxford University Press. ISBN 0-19-855386-2
5. Hiemenz, P. C., Rajagopalan, R., (1997). Principles of Colloid and Surface Chemistry Marcel Dekker Inc., New York. ISBN 0-8247-9397-8
6. Moore, W.J. (1963). Physical Chemistry 4th ed. Longman publishers/London/Prentice Hall, NJ.

See also

Physical chemistry portal

Sub-topics

• Photochemistry
• Thermochemistry
• Chemical kinetics
• Quantum chemistry
• Electrochemistry
• Surface chemistry
• Solid-state chemistry
• Spectroscopy
• Materials science
• Physical organic chemistry
• Membrane Formation
• Micromeritics

Publications

• Important publications in physical chemistry(chemistry),
• Important publications in physical chemistry(physics)

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