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In this video I'm going to briefly
describe
the
meaning for the
different regions in
the dividing lines on a pressure temperature diagram.
So in this case we're plotting the log of the pressure just
to show the behavior at high pressures in
a little more clear. A couple of things that are important to keep in mind if we look at
this diagram this is not
a diagram that is holding something like volume constant
but instead this is a projection of a three-dimensional
pressure-volume temperature diagram
so if we had a 3-D structure and we looked at it end on
we see these dividing lines. First let's look at the region's
solid here at higher pressures and lower temperatures
Vapor lower pressures higher temperatures
and liquid and so these lines that divide for example
this line that divides the liquid from the vapor
is the phase line where we have a phase change were we cross this lines so
as we go from a my point here for example
to a point here at constant temperature by lowering the pressure
we're going to see a big change in volume. Change in energy we had to
put energy in
to make this phase transition occur. Everything occurs right at
this pressure and this temperature. Another thing that's important to keep in mind
this is the critical point so this line
ends which means there's no real distinction
as we go from here over to here between liquid and vapor
this region up here instead of referring to as a liquid or vapor
it's a super-critical fluid however in contrast the line that divides the solid and the
liquid and this line is the same thing if we were
at high pressure in a constant temperature and we lowered the pressure
for this material we go from a solid to a liquid
the transition happened at one pressure for this temperature
but this line doesn't end.
It continues and in real systems
there may be other branches from this because they're different solid phases
as we go to higher pressures but we are just looking at one solid phase here
Let's look at a couple other aspects of this diagram
remember if this is a solid and this is a vapor
then we can go from a solid-phase into the vapor phase
without liquid forming. We have the phase transition again
at one temperature for this particular pressure
and so we get sublimation. Let's look at one more aspect and mention
that we can go from the liquid
to the solid by increasing the pressure
this is a behavior we'll see from most materials for example for carbon dioxide
however
the curve looks different for water in liquid
solid now. This says if we increased the pressure we go from solid to liquid
as opposed to going from liquid to solid. So water and
very few materials have this particular
behavior but is important property of water to makes a significant
different. Other properties were familiar with waters
critical point, triple point
which is very near zero degrees C.