The Internal Energy as a State Function Video Lecture | Chemistry Class 11 - NEET

Hey it's professor Dave, let's define internal energy.
We now understand
temperature as a measure of the
molecular kinetic energy present in the
particles of a substance. As we said, this
kinetic energy is distributed amongst
translational motion, rotational motion
and vibrational motion. There is also
molecular potential energy by virtue of
the electromagnetic force acting amongst
the atoms of an individual molecule and
between each separate molecule. The sum
of all of these types of energy that are
exhibited by the particles of a
substance is called the internal energy
of that substance, represented by an
upper case U. This is the energy
associated with atomic motion and it is
a quantity that is directly proportional
to the temperature of a sample. Higher
temperatures mean more internal energy,
lower temperatures mean less internal
energy. In this way, we must understand
that a substance does not contain heat,
it contains internal energy, like the
kinetic energy of all the particles, and
it is the transfer of this energy from
areas of high temperature to areas of
low temperature that we can label as
heat. Internal energy is an important
concept in the study of thermodynamics
which is the study of heat and
temperature and their relation to energy
and work. The internal energy of a system
can be increased due to heat transfer
but also due to things like friction or
structural deformation when bending a
piece of metal or stretching a rubber
band. But as we learned earlier, for a
particular system there will always be
conservation of energy. We already know
about the kinetic energy and potential
energy of an object moving through a
gravitational field so let's add the
internal energy of the particles in the
object to this list, and restate
conservation of energy with the
following equation: change in potential
energy plus
change in kinetic energy plus change in
internal energy will always be zero. That
means that whenever there is a change in
any one of these quantities the
difference in energy must transform into
or be provided by one of the other forms.
So when two objects participate in an
inelastic collision, some of the kinetic
energy is transferred into internal
energy, which will be absorbed by the
object. Internal energy can in turn be
used to do work through heat transfer,
pressure-volume work by an expanding gas
or some other process. We should also
note that internal energy is a state
function, which means that the internal
energy of a system depends only on the
state of the system and not how it got
to that state. We will learn more about
state functions later. These kinds of
concepts are precisely what we will be
examining when we discuss the laws of
thermodynamics, so let's move on to this
incredibly important subject.
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