Boiling Water with an Ice Cube: Demonstration of Vapor Pressure
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- เผยแพร่เมื่อ 26 พ.ย. 2014
- MEC516/BME516 Fluid Mechanics: Vapor pressure demonstration using a mason jar of saturated water. This video is also relevant in introductory thermodynamics courses.
Course Textbook: F.M. White and H. Xue, Fluid Mechanics, 9th Edition, McGraw-Hill, New York, 2021.
#fluidmechanics #thermodynamics #vaporpressure
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All the videos (and pdf downloads) for this introductory Fluid Mechanics course are available at: www.drdavidnaylor.net/
Perfect demonstration sir. Theory to practical, very important for every Mechanical Engineering student. Thank you.
Mechanical engineering student here. I've done tons of saturated liquid/vapor problems in thermodynamics, but this really brings it to life. Great demonstration!
I agree that this is an odd term. I think it refers to liquid phase as being "saturated" with thermal energy. If you add heat at constant pressure, the temperature of the liquid phase does not increase. The liquid has all the thermal energy it can hold at that pressure.
When it's boiling, the water is cooling but does that mean the space above is getting warmer?
Love this! Useful for my meteorology students. Thank you.
Awesome video for clearing concept for thermodynamics..I have completed my engineering but still didn't know this concept. Thankyou very much sir 👏❤️
Thank you, much appreciated
I did this with my seventeen year old and my six year old and I felt like the coolest mom ever!
So glad it worked. Science!
Nice a good demonstration .
Excellent video for teaching vapor pressure. Easy and handy example.
no
Really really nice and interesting!!
Thank you. Good demonstration
Thanks! This really helped for Chemistry class.
A great visualization!
I love it
Ty for the info 👉👈
So cool
Cool. So if you heat it up again, could you see the condensation? Like in a cloud chamber?
Please also second question what is the difference between steam, gas, vapor, dew, humidity ?
Very very nice
Sir,is it necessary to not have any trace of air in jar.because in definition of vapor pressure "The vapor pressure Pv of a pure substance is defined as the pressure
exerted by its vapor in phase equilibrium with its liquid at a given temperature." i am confused that whether there is only vapor is there above liquid OR there is air fully saturated with vapor which is in equilibrium with liquid?please clear this doubt.
What season can this experiment be related to ? Why
I would like to use dry ice with this demonstration
Why does vapor pressure increase if you put ice?
very interesting video sir ... 😊👍
Glad to hear it was helpful
Quick question, what is the saturated water in the video saturated with?
Thermal energy.
if you let the water cool to room temperature, and then place the ice cube... Will it continue to bubble
Unfortunately, no. The condensation rate is too low at room temperature.
I wonder if I understand well ??? when liquid will reach room temp and you put the ice on top, vapor will still change to liquid on the surface of the metal and bubbles will form in the liquid in much slower rate. it will be happening until liquid temp will droop close to 0C and we will have ice formation. no more saturation. :((am I right ????
It will remain saturated until the triple point (about 0.01C).
thanks~ I have one question. in that bottle, I think at first pressure of water vapor is 1atm
but before you put ice, is pressure of water vapor at the vapor pressure in equilibrium?
what i wondering is pressure in the bottle before you put ice
Immediately after putting on the lid, the liquid and vapor are a equilibrium at saturation conditions, 1atm and 100C. As the water cools the pressure will fall. But the cooling process is slow enough (without the ice) that the system will be very close to equilibrium. For example, if you measured the liquid temperature before putting on ice -- say, it was 95C -- you could look up the corresponding pressure on a saturation table (84.6kPa). This would be very close to the actual pressure in the vapor in the top of the jar. (I've thought about adding a Bourdon gage on the lid to demonstrate this.) Of course, the system is not at perfect equilibrium, since there is some vapor condensation on the glass and lid without the ice. But it would be close.
One thing still I still get confused about vapor pressure:
Lets say I pressurized the jar with compressed gas to 2 atm (gauge pressure).
At 2 atm, the boiling point of water is 120 'C.
So at this point, I will heat the water to 125 'C to make it boil. As it boils, should I expect the vapor to exert a pressure into the enclosed system? Should I expect to see the pressure gauge go above 2 atm? If so, is it possible to predict the pressure increase?
The reason I'm confused is due to the word 'pressure' in vapor pressure.
The pressure in steam tables is absolute pressure. A gauge pressure of 2 atm corresponds to an absolute pressure of 3 atm (if local atmospheric pressure is ~1 atm). At this absolute pressure, the saturation temperature ("boiling point") is about 134 C (not 120 C).
Thanks David. I see... So if I heat the water to above 135 C and get it boiling, would I see an increase in the pressure of the system? As in, does the boiling vapor "add" more pressure?
Yes. If you have saturated water at 3 atm (134C) in a sealed jar and you add heat, the pressure will increase. Have you taken a thermodynamics course? If so, this process is a vertical upward line on a T-v diagram. This is a constant specific volume process. Hope that helps. (Also, remember the physical cause of pressure: It is the force produced by water molecules bouncing off the container walls. More heat means more molecular kinetic energy, means more impact force, and thus, higher pressure on the walls.)
I see! That makes sense. I have done a subject on thermodynamics but never really understood it well, but thanks for pointing that out! at least now I know where to do further reading (T-V diagrams). Thanks again for your replies. It's really helped
Hey, i have a question:
Why do we have to wait before putting ice on top of it? It didnt work when tried instantly after taking it from oven.
The timing of the ice should not matter. However, it is critically important not to let air into the jar. Even a small amount of air will greatly reduce the condensation rate on the lid, and reduce the tendency to boil. So, differences in the haste and care in putting on the lid can produce a lot of variability. That may be what you are seeing.
question, how many minutes to boil water in the microwave?
I'd say about 60 to 90 seconds if sufficient. The air needs to be almost completely replaced by water vapor. The presence of any air greatly reduces the heat transfer rate to the lid, and reduced the effect.
thanks for demo
Would the water bonds break into H and o2
No. This process does not break chemical bonds.
you mean you lower the temperature by adding ice to increase the temperature of water? how does thermodynamics work here?
Boiling doesn’t mean increasing the temperature. Boiling starts, when vapour pressure of the liquid becomes equal to the atmospheric pressure. Boiling can occur at 20 degree celsius also.
Still I did not understand what is SATURATED LIQUID NOT SATURATED GAS :( but good illustration of equilibrium.
Is the water hot?
Yes. It sets off at the normal boiling point (100C, 212F) at atmospheric pressure, and cools to about 50C (120F), still boiling because the pressure drops in the jar.
Isn't this how those bubbling Christmas lights work?
Yes, I think so, though it is probably not water.
mi profe de termo me mandó aqui :B
tacobell
Sir, I tried the experimentation exactly as you illustrated, but I didn't come up with the same result, like yours.
Hmmm... what could go wrong? Try it again and be extra careful to get all the air out of the upper part of the jar. Don't poke many holes in the cling film and let it boil for a couple of minutes. Then get the lid on FAST. For technical reasons that I can't go into here, you need almost pure water vapor in the upper space. Even a bit of air will reduce the condensation rate tremendously and may prevent vigorous boiling. Hope that helps.
@@FluidMatters Thank you so much, sir, you're my lifesaver huhuhuhu