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Let’s stop to think about why this is true at 1 atm pressure. To do so, we need to remember how we observed the boiling point. We applied a pressure using a piston which trapped a liquid in a cylinder. When we elevated the temperature, we observed a phase transition at one temperature which we called the boiling point. At that point, the vapor became stable. For this to be true, the pressure created by the vapor (which is of course the vapor pressure) must at least be equal to the pressure applied externally to the piston. If the vapor pressure is less than the applied pressure, the vapor cannot resist the applied pressure, the piston moves in, and all of the vapor condenses into the liquid. Therefore, for the liquid to boil, the temperature must be high enough for the vapor pressure to equal the applied pressure. Only at this temperature or above will the rate of evaporation be great enough to offset the rate of condensation created by the externally applied pressure.

To find the boiling point temperature at 1 atm pressure, we need to find the temperature at which the vapor pressure is 1 atm. To do so, we find the point on the graph where the vapor pressure is 1 atm and read off the corresponding temperature, which must be the boiling point. Of course, this will work at any given pressure. We just read off of Figure 1 the temperature at which the vapor pressure equals the applied pressure, and that will be the temperature at which the liquid boils at that pressure. This means that Figure. 1 gives us both the vapor pressure of water as a function of the temperature and the boiling point temperature of water as a function of the applied pressure. They are the same graph!

Remember that in the experiment, at the boiling point we observed that both liquid and gas are at equilibrium with one another. Both phases are present at the boiling point. This is true at every combination of applied pressure and boiling point temperature. Therefore, for every combination of temperature and pressure along the curve on the graph in Figure 1, we observe liquid-gas equilibrium.

What happens at combinations of temperature and pressure which are not on the line drawn in Figure 1? To find out, let’s run the experiment. We first start at any temperature-pressure combination on the curve and elevate the temperature while holding the applied pressure constant. In Figure 1, this moves us to the right of the curve. We observe that all of the liquid vaporizes, and there is only gas in the container. What happened to the equilibrium? At higher temperature, the vapor pressure of the liquid rises, but if the applied pressure does not also increase, then the vapor pressure will be greater than the applied pressure. The vapor pushes back the piston and the liquid evaporates. We must therefore not be at equilibrium anymore. For all temperature and pressure combinations to the right of the curve, only vapor exists.

Now let’s start at a point on the curve and lower the temperature while holding the pressure constant, leaving us to the left of the curve. We observe that all of the gas condenses into the liquid. This is because the vapor pressure is below the applied pressure, and the piston moves in against the gas until it all condenses into the liquid. For all temperature and pressure combinations to the left of the curve, only liquid exists.

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
how to synthesize TiO2 nanoparticles by chemical methods
Zubear
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Concept development studies in chemistry 2013. OpenStax CNX. Oct 07, 2013 Download for free at http://legacy.cnx.org/content/col11579/1.1
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