The Kinetic Molecular Theory of Gas II - Gaseous Video Lecture | Chemistry for GRE Paper II

let's think about these rules a little
bit deeper to explain a few properties
of gases on that are unique to gases we
don't see these properties in solids or
liquids here's the first one let's
assume that I have a container of gas
just like I had at the beginning of the
lesson and I have some gas particles in
it this is we said before here the gas
particles now remember these gases of
course are in constant random motion and
they're balanced against each other
they're bouncing against the sides of
containers that's what these arrows are
indicating obviously they're all moving
but I'm only drawing a few arrows when
we talked about this the very beginning
of the lesson we drew a container that
had a top on it let's imagine what
happens when we open that top if we can
lift it up well
these gases are in random motion and
they only really change directions when
they hit against the side of the
container and so what that's going to
mean is eventually these guys are are
going to bounce their way out of the
container and they're going to spread
out I mean imagine that we had a tiny
little room filled with hyperkinetic
little kids and we open the door the
kids wouldn't all stay in the room
they'd eventually move on out bounce
against the walls bounce against each
other until they filled as a big of a
space as we gave them this is what we
call expandability expandability because
gases will move around they'll expand to
fill any area that we give them so let's
assume that this whole area here is a
new container we open the old one these
guys are going to move out they're going
to be randomly moving until they fill
this whole area it's what we call
expandability because they expand to
fill a new volume now the process of
these gases moving out is what we call
diffusion you're familiar with the
concept of diffusion even if you don't
necessarily know what causes it or if
you're not familiar with the technical
name diffusion is the reason why when
you're at one end of the mall and the
movie theaters on the other end you
still smell popcorn
you get hungry over at the movie theater
they're making popcorn and the the gas
odor or fragrance of popcorn those gas
particles are moving around they're
moving around very fast and they diffuse
out from their original location because
of that they can reach you all the way
down at the other end of the mall
because those gas particles that make up
the popcorn scent are going to spread
out to fill as large of a volume as you
give them so that's expandability a very
important quality of gas you don't see
if the solids you don't see the liquids
let's look at another quality again here
we have a container of gas let's put
some gas particles in there remember
though we're worried these guys might
get out they're going to expand if we
don't close this container so what I'm
going to put here is I'm going to put a
plunger or a piston here so we can think
about this container as a like a barrel
or a cylinder so this piston is
something that I can grab on to and I
can move it in this direction let's look
at what happens when I do that up here
is it before here's the after I've moved
the piston all the way in here and what
I've done is I've pressed all of these
gas particles closer together so here
they are now why can I do this I can do
this because of the first rule that we
talked about in our kinetic theory of
gases and that's the gas particles are
tiny and there's a tremendous amount of
empty space around them because there's
so much empty space I can really squeeze
these guys into a much smaller volume
here we call this compressing it and
this quality of gasses is known as
compressibility compressibility is
particularly important like if you're
into scuba diving what we can do is we
can take a very large quantity of air
and we can squeeze all the particles
that make up that air into a tank which
can allow you to breathe for a very long
period of time the particles are very
very very very pressed together or
compressed now compressibility is unique
to gases
uh if I took a big hunk of metal and I
tried to press down on it with a whole
bunch of pressure it wouldn't change its
size sometimes people think that liquids
are compressible but they're not I could
take a piston and a cylinder like this
and fill it with water and try to jam
down on that plunger nothing's going to
happen
I can't compress the particles in liquid
I can compress them a tiny bit but not
very much gas is on the other hand I can
really cram them in a tank or I can cram
them in a cylinder like this because
that because there's so much space in
between them they can really pack
together this compressibility and
expandability are two unique
characteristics that we only see in
gases so we looked at kinetic energy
today and different states of matter and
then we looked at the molecular kinetic
molecular theory of gases some rules
that gases abide by finally looked at
expandability and compressibility this
is all the foundation that we need now
on to delve further into gases and start
looking at conceptual problems and
mathematical calculations for gas