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Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of
physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Physical science is that depar ...
such as motion,
energy In physics, energy (from Ancient Greek: wikt:ἐνέργεια#Ancient_Greek, ἐνέργεια, ''enérgeia'', “activity”) is the physical quantity, quantitative physical property, property that is #Energy transfer, transferred to a phy ...
,
force In physics, a force is an influence that can change the motion of an Physical object, object. A force can cause an object with mass to change its velocity (e.g. moving from a Newton's first law, state of rest), i.e., to accelerate. Force can ...
,
time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...
,
thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...
, quantum chemistry, statistical mechanics,
analytical dynamics In classical mechanics, analytical dynamics, also known as classical dynamics or simply dynamics, is concerned with the relationship between Motion (physics), motion of bodies and its causes, namely the force (physics), forces acting on the bodies ...
and chemical equilibria. Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a supra-molecular science, as the majority of the principles on which it was founded relate to the bulk rather than the molecular or atomic structure alone (for example, chemical equilibrium and colloids). Some of the relationships that physical chemistry strives to resolve include the effects of: #
Intermolecular force An intermolecular force (IMF) (or secondary force) is the force that mediates interaction between molecules, including the Electromagnetism, electromagnetic forces of attraction or repulsion which act between atoms and other types of neighbouring ...
s that act upon the physical properties of materials ( plasticity,
tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials ...
,
surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...
in
liquid A liquid is a nearly Compressibility, incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of State of matter#Four fundamental states, the four fund ...
s). # Reaction kinetics on the rate of a reaction. # The identity of ions and the
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
of materials. # Surface science and
electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between Electric potential, electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential dif ...
of
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the cytoplasm, interior of all Cell (biology), cells from th ...
s. # Interaction of one body with another in terms of quantities of
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
and work called
thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...
. # Transfer of heat between a chemical system and its surroundings during change of phase or
chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
taking place called thermochemistry # Study of colligative properties of number of species present in solution. # Number of phases, number of components and degree of freedom (or variance) can be correlated with one another with help of phase rule. # Reactions of
electrochemical cell An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic o ...
s. # Behaviour of microscopic systems using
quantum mechanics Quantum mechanics is a fundamental Scientific theory, theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including qua ...
and macroscopic systems using statistical thermodynamics.


Key concepts

The key concepts of physical chemistry are the ways in which pure
physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Physical science is that depar ...
is applied to chemical problems. One of the key concepts in classical chemistry is that all
chemical compounds A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A homonuclear molecule, molecule co ...
can be described as groups of
atoms Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, l ...
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.Atkins, Peter and Friedman, Ronald (2005). ''Molecular Quantum Mechanics'', p. 249.
Oxford University Press Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print books ...
, New York. .


Disciplines

Quantum chemistry, a subfield of physical chemistry especially concerned with the application of
quantum mechanics Quantum mechanics is a fundamental Scientific theory, theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including qua ...
to chemical problems, provides tools to determine how strong and what shape bonds are, how nuclei move, and how light can be absorbed or emitted by a chemical compound.
Spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectrum, electromagnetic spectra that result from the interaction between Electromagnetism, electromagnetic radiation and matter as a function of the wavelengt ...
is the related sub-discipline of physical chemistry which is specifically concerned with the interaction of
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
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 Chemical thermodynamics is the study of the interrelation of heat and Work (thermodynamics), work with chemical reactions or with physical changes of thermodynamic state, state within the confines of the laws of thermodynamics. Chemical thermodynam ...
, which sets limits on quantities like how far a reaction can proceed, or how much
energy In physics, energy (from Ancient Greek: wikt:ἐνέργεια#Ancient_Greek, ἐνέργεια, ''enérgeia'', “activity”) is the physical quantity, quantitative physical property, property that is #Energy transfer, transferred to a phy ...
can be converted into work in an
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combust ...
, and which provides links between properties like the thermal expansion coefficient and rate of change of
entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
with
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
for a gas or a
liquid A liquid is a nearly Compressibility, incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of State of matter#Four fundamental states, the four fund ...
. 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.Hill, Terrell L. (1986). ''Introduction to Statistical Thermodynamics'', p. 1. Dover Publications, New York. . 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 Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with chemical thermodynamics, which deals with the direction in wh ...
, 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 In physics, energy (from Ancient Greek: wikt:ἐνέργεια#Ancient_Greek, ἐνέργεια, ''enérgeia'', “activity”) is the physical quantity, quantitative physical property, property that is #Energy transfer, transferred to a phy ...
than either the reactants or the products and serve as a barrier to reaction. In general, the higher the barrier, the slower the reaction. A second is that most chemical reactions occur as a sequence of elementary reactions, 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,Chandler, David (1987). ''Introduction to Modern Statistical Mechanics'', p. 54. Oxford University Press, New York. . 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.


History

The term "physical chemistry" was coined by Mikhail Lomonosov in 1752, when he presented a lecture course entitled "A Course in True Physical Chemistry" () before the students of Petersburg University. 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 Chemical thermodynamics is the study of the interrelation of heat and Work (thermodynamics), work with chemical reactions or with physical changes of thermodynamic state, state within the confines of the laws of thermodynamics. Chemical thermodynam ...
,
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electron The electron ( or ) is a subatomic particle with a negative one elementary charge, elementary electr ...
s in solutions,
chemical kinetics Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with chemical thermodynamics, which deals with the direction in wh ...
and other subjects. One milestone was the publication in 1876 by
Josiah Willard Gibbs Josiah Willard Gibbs (; February 11, 1839 – April 28, 1903) was an American scientist who made significant theoretical contributions to physics, chemistry, and mathematics. His work on the applications of thermodynamics was instrumental in t ...
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. The first
scientific journal In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. Content Articles in scientific journals are mostly written by active scientists such ...
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, 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 ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...
between 1901 and 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 Quantum mechanics is a fundamental Scientific theory, theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including qua ...
into quantum chemistry from the 1930s, where
Linus Pauling Linus Carl Pauling (; February 28, 1901August 19, 1994) was an American chemist, biochemist, chemical engineer, peace activist, author, and educator. He published more than 1,200 papers and books, of which about 850 dealt with scientific topi ...
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 Spectroscopy is the field of study that measures and interprets the electromagnetic spectrum, electromagnetic spectra that result from the interaction between Electromagnetism, electromagnetic radiation and matter as a function of the wavelengt ...
, such as
infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption spectroscopy, absorption, emission spectrum, emission, or reflection (physics), reflection. ...
, 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, 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), 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


Journals

Some journals that deal with physical chemistry include '' Zeitschrift für Physikalische Chemie'' (1887); '' Journal of Physical Chemistry A'' (from 1896 as ''Journal of Physical Chemistry'', renamed in 1997); '' Physical Chemistry Chemical Physics'' (from 1999, formerly '' Faraday Transactions'' with a history dating back to 1905); '' Macromolecular Chemistry and Physics'' (1947); '' Annual Review of Physical Chemistry'' (1950); '' Molecular Physics'' (1957); '' Journal of Physical Organic Chemistry'' (1988); '' Journal of Physical Chemistry B'' (1997); '' ChemPhysChem'' (2000); '' Journal of Physical Chemistry C'' (2007); and '' Journal of Physical Chemistry Letters'' (from 2010, combined letters previously published in the separate journals) Historical journals that covered both chemistry and physics include '' Annales de chimie et de physique'' (started in 1789, published under the name given here from 1815 to 1914).


Branches and related topics

*
Chemical thermodynamics Chemical thermodynamics is the study of the interrelation of heat and Work (thermodynamics), work with chemical reactions or with physical changes of thermodynamic state, state within the confines of the laws of thermodynamics. Chemical thermodynam ...
*
Chemical kinetics Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with chemical thermodynamics, which deals with the direction in wh ...
* Statistical mechanics * Quantum chemistry *
Electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between Electric potential, electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential dif ...
* Photochemistry * Surface chemistry * Solid-state chemistry *
Spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectrum, electromagnetic spectra that result from the interaction between Electromagnetism, electromagnetic radiation and matter as a function of the wavelengt ...
* Biophysical chemistry *
Materials science Materials science is an interdisciplinary Interdisciplinarity or interdisciplinary studies involves the combination of multiple academic disciplines into one activity (e.g., a research project). It draws knowledge from several other field ...
* Physical organic chemistry * Micromeritics


See also

* List of important publications in chemistry#Physical chemistry * List of unsolved problems in chemistry#Physical chemistry problems * Physical biochemistry * :Physical chemists


References


External links


The World of Physical Chemistry
(Keith J. Laidler, 1993)
Physical Chemistry from Ostwald to Pauling
(John W. Servos, 1996)

(Joachim Schummer, ''The Autonomy of Chemistry'', Würzburg, Königshausen & Neumann, 1998, pp. 135–148)
The Cambridge History of Science: The modern physical and mathematical sciences
(Mary Jo Nye, 2003) {{Authority control