
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 10
23) 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)
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