physical chemistry is the study of
macroscopic atomic subatomic and
particulate phenomena and 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 dynamics and
equilibrium physical chemistry in
contrast to chemical physics is
predominantly but not always a
macroscopic or super molecular science
as the majority of the principles on
which physical chemistry was found in
our concepts related to the bulk rather
than on molecular / atomic structure
alone for example chemical equilibrium
and colloids 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
bonds is one is a major goals of
physical chemistry to describe the atoms
and bonds precisely it is necessary to
know both where the nuclear 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
in what shape bonds are how nuclear ov
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 and equilibrium and reversible
changes and not what actually does
happen or how fast away from equilibrium
which reactions to 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 and 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 the
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
instant 6x 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 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