State variables types - Thermodynamics Video Lecture - Class 11

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thermodynamics part 5 is brought to you
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please make sure that you have watched
all the videos from part 1 to part 4
before going ahead with part 5 now we
will talk about thermodynamics state
variables so what a thermodynamic state
variables this is a basic top topic
which needs to be explained at the
beginning so that you don't have the
issues when we go ahead and we talk
about first law of thermodynamics and
second law of thermodynamics and their
applications thermodynamic state
variables are the macroscopic quantities
determining the thermodynamic
equilibrium state of a system so oh I
told you that thermodynamics is
completely based on these macroscopic
quantities in thermodynamics we study
the different laws of thermodynamics
which errors or which describe the
behavior of various thermodynamic
systems in terms of certain macroscopic
quantities so these macroscopic
quantities are known as thermodynamic
state variables why are they known as
thermodynamic state variables since it
is really since they describe the
behavior of thermodynamic system so they
are called thermodynamic so from there
we get from thermodynamics we get this
term thermodynamic why is this term
state the term steam implies that these
macroscopic quantities determine the
speed of a system what I want do I mean
by state of a system state is nothing
but the condition of the system at a
particular instant of time that is what
is the pressure volume and temperature
of the system at one particular time so
stick these variables basically tell us
the state of the system so they are
known as thermodynamic state variables
right for example pressure temperature
volume mass internal energy they are all
thermodynamic state variables right with
help of these variables we can tell you
the state of a particular substance that
I mean suppose if I say that this gas is
at a temperature of at temperature T
degree Celsius and with a volume of
these centimeter cube so this tells you
the position or the condition of the gas
at that particular time so this pressure
temperature volume mass internal energy
they are all thermodynamic state
variables a system not in equilibrium
cannot be described by state variables
why that's very obvious because if a
system is not in equilibrium that means
these variables were very beginning I
explained you what is equilibrium in in
thermodynamics equilibrium would mean
that the macroscopic variables will not
change with time right now suppose if a
system is not in equilibrium that means
such quantities such macroscopic
quantities like pressure temperature or
volume they are continuously changing
with time now see if these values itself
are changing with time then how can we
describe the system with the help of
these variables like sometimes your
pressure will be busy sometimes the
pressure will be to be sometime it will
be 3 P sometimes it will be 40 so I just
cannot describe and this change will
happen continuously if the system is not
in equilibrium so we cannot describe a
system which is not in equilibrium by
state variables right so these
thermodynamic state variables are often
known as just state variables so these
state variables determine the
thermodynamic equilibrium state of
system they are macroscopic quantities
their common examples are pressure
volume temperature now there are various
types of thermodynamic state variables
basically there are two types of
thermodynamic state variables extensive
variables is the first category
extensive variables indicate the size of
the system
so extensive state variables they depend
on mass of the system or the number of
particles size of the system means what
whenever I talk of any system the size
will mean either the mass of the system
or the number of particles in the system
so extensive variables are those which
depend on the size of the system so
examples of extensive variables would be
volume examples of extensive variables
would be volume mass internal energy if
you see all of them depend on the size
of the system for example mass mass
depends on size of the system greater
the size greater the mass right
similarly volume
similarly internal energy internal
energy is again there's some what is
internal energy we will talk about
internal energy in another two to three
sides ahead so we will see that all
these variables are dependent on the
size of the system so they are quite
extensive variables the other category
is intensive variables so it's very
obvious now if extensive variables are
the one which depends on size of the
system intensive variables will be those
which will not depend on size of the
system so they does not indicate size of
the system they have they have nothing
to do with the number of particles in
the system or the mass of the system so
such variables are temperature pressure
so pressure and temperature fall and
then intensive variables and volume mass
internal energy they fall under
extensive variables thank you please
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