Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena
in chemical systems in terms of laws and concepts of physics.
It applies the principles, practices and concepts of physics such as motion, energy, force,
time, thermodynamics, quantum chemistry, statistical mechanics and dynamics, equilibrium.
Physical chemistry, in contrast to chemical physics, is predominantly a macroscopic or
supra-molecular science, as the majority of the principles on which physical chemistry
was founded, are concepts related to the bulk rather than on molecular/atomic structure
alone.
For example, chemical equilibrium, and colloids.
Some of the relationships that physical chemistry strives to resolve include the effects of:
Intermolecular forces that act upon the physical properties of materials.
Reaction kinetics on the rate of a reaction.
The identity of ions and the electrical conductivity of materials.
Surface chemistry and electrochemistry of membranes.
Interaction of one body with another in terms of quantities of heat and work called thermodynamics.
Transfer of heat between a chemical system and its surroundings during change of phase
or chemical reaction 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 can be correlated with one
another with help of phase rule.
Reactions of electrochemical cells.
Key concepts 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.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, how nuclei
move, and how light can be absorbed or emitted by a chemical compound.
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.
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.
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.
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 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, 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 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, Gibbs phase rule.
Other milestones include the subsequent naming and accreditation of enthalpy to Heike Kamerlingh
Onnes and to macromolecular processes.
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, these were the leading figures in physical chemistry
in the late 19th century and early 20th century.
All three were awarded with 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,
EPR spectroscopy and NMR 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, more recent discoveries in astrochemistry,
as well as the development of calculation algorithms in the field of "additive physicochemical
properties", and in this area is concentrated practical importance of contemporary physical
chemistry.
See Group contribution method, Lydersen method, Joback method, Benson group increment theory,
QSPR, QSAR Journals
Some journals that deal with physical chemistry include:
Zeitschrift für Physikalische Chemie Journal of Physical Chemistry A
Physical Chemistry Chemical Physics Macromolecular Chemistry and Physics
Annual Review of Physical Chemistry Molecular Physics
Journal of Physical Organic Chemistry Journal of Physical Chemistry B
ChemPhysChem Journal of Physical Chemistry C
Journal of Physical Chemistry Letters Historical journals that covered both chemistry
and physics include Annales de chimie et de physique.
Branches and related topics
See also
List of important publications in chemistry#Physical chemistry
List of unsolved problems in chemistry#Physical chemistry problems
Category:Physical chemists References
External links Physical Chemistry
The World of Physical Chemistry Physical Chemistry from Ostwald to Pauling
100 Years of Physical Chemistry Physical Chemistry: neither Fish nor Fowl?
Cathedrals of Science The Cambridge History of Science: The modern
physical and mathematical sciences