Introduction to Photochemistry Video Lecture

give a brief introduction to
photochemistry photo chemistry is the
study of chemical reactions that proceed
with the absorption of light radiation
by atoms or molecules some common
examples of such reactions involving
photo chemistry include photosynthesis
of carbohydrates and plants conversion
of oxygen into ozone and the formation
of vitamin D with sunlight all such
reactions that occur with absorption of
radiations or photons are called
photochemical reactions some typical
photochemical reactions include
dissociation reactions rearrangement
reactions addition reactions
polymerization reactions combination
reactions decomposition reactions
substitution reactions basically photo
chemistry is mainly involved with rates
and mechanisms of reactions which are
caused due to exposure to radiant energy
which lies in the ultraviolet and
visible range of spectrum which ranges
from two thousand angstrom to eight
thousand angstrom wavelength let's
discuss how photochemical reactions are
different from other reactions we know
that ordinary reactions which are caused
due to molecular collisions are called
thermal or dark reactions all such
spontaneous thermal reactions are
generally accompanied by a decrease in
free energy whereas photochemical
reactions are accompanied by an increase
in free energy also generally the rate
of most of the thermal reactions is very
slow because only those molecules which
have an excess of energy can undergo
chemical reaction on the other hand rate
of photochemical reactions is very fast
as they depend on an outside source for
their energy in photochemical reactions
molecules are activated by absorption of
photons of
particular frequency and Waveland it is
also important to note that all
photochemical reactions take place in
two stages in the first stage which is
also known as primary process the
reacting molecule undergoes activation
by absorption of light in the second
stage which is known as secondary
process the activated molecules undergo
a photochemical change the main
differences between photochemical
reactions and thermo chemical reactions
can be stated in the form of a table