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InvisibleTODAY
Battletoad
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Registered: 09/25/03
Posts: 10,218
Loc: Metropolis City, USA
Pressure and boiling point
    #5941928 - 08/07/06 07:45 PM (17 years, 5 months ago)

Well geewhiz, it's science day at my house!!

I decided I would conduct an experiment today.

Purpose: To determine the relationship between pressure and boiling point.

Method:

1.  Measured two 125mL of water and poured into identical containers and let sit for a few hours to gaurantee that they match room temperature.

2.  Measured the temperature of the room at 32.1 Celsius. 

3.  Poured one of the cups of water into my pressure cooker which has been sitting in the same room and therefore at the same temperature.

4.  Put the pressure cooker, uncovered, on the power burner so that the center of the ring of flames was at the center of the bottom of the pressure cooker.

5.  Turned the power burner on as high as it will go before the ignitor starts clicking (as a benchmark for the next trial).

6.  Timed exactly 360 seconds until all of the water had vaporized.

***Didn't actually do it because I decided it would be too dangerous***

Repeat steps 3-6 but put the lid on the pressure cooker.  When 360 seconds expires (and this is why it is too dangerous) remove the lid of the pressure cooker, exposing the contents of the pressure cooker to the pressure of the room.

I wanted to know if the pressure differential would vaporize all of the water even if it was in a liquid state inside the pressurized container.  I theorize (experimental error being neglected) that all of the water would indeed vaporize.  In theory, am I correct?

:eek:


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ca'rouse (k-rouz)
intr.v.
To engage in boisterous, drunken merrymaking.


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InvisibleBanez
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Re: Pressure and boiling point [Re: TODAY]
    #5941996 - 08/07/06 07:58 PM (17 years, 5 months ago)

i didnt read the experiment but they are inversley related.. i believe.. as you increase pressure... liquids have a lower boiling point


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Banez' PF Tek For Beginners


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InvisibleTODAY
Battletoad
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Posts: 10,218
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Re: Pressure and boiling point [Re: Banez]
    #5942313 - 08/07/06 09:20 PM (17 years, 5 months ago)

Actually...No, as you increase pressure, boiling point increases, that is temperature required to boil a liquid increases under increased pressure.


--------------------

ca'rouse (k-rouz)
intr.v.
To engage in boisterous, drunken merrymaking.


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InvisibleBanez
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Re: Pressure and boiling point [Re: TODAY]
    #5942364 - 08/07/06 09:39 PM (17 years, 5 months ago)

shit im high.. lol.. i just thought we did something in chem.. i just got em switched up


--------------------
Banez' PF Tek For Beginners


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InvisibleTODAY
Battletoad
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Registered: 09/25/03
Posts: 10,218
Loc: Metropolis City, USA
Re: Pressure and boiling point [Re: Banez]
    #5942370 - 08/07/06 09:41 PM (17 years, 5 months ago)

you got them switched up...but at least you were thinking about it!! Go thought!! :grin:


--------------------

ca'rouse (k-rouz)
intr.v.
To engage in boisterous, drunken merrymaking.


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InvisibleColonel Kurtz Ph.D
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Re: Pressure and boiling point [Re: TODAY]
    #5942399 - 08/07/06 09:52 PM (17 years, 5 months ago)

If I understand your question right and that's a big IF right now, I'd say in those exact conditions that would work as you said, but it might not with bigger quantities of water because after all, more pressure=more molecule collisions which would create way more hidrogen bonds between molecules than non-pressured heating, thus changing the global ammount of heat needed for the same goals.

On the other hand that pressure would give more kinetic energy to the molecules thus increasing evaporation rate... :shrug:

Let's just say that I've never heard or even thought about something like you just said, so I may be talking out of my ass actually :grin:
Interesting Q tho.


--------------------
:whatwhat:

There's no better way to rock out than with your cock out!!


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InvisibleZippoZM
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Re: Pressure and boiling point [Re: TODAY]
    #5942404 - 08/07/06 09:54 PM (17 years, 5 months ago)

most likely as soon as you were to open the pressure cooker, the pressure inside would drop rapidly, as would the boiling point, so whatever was water would become steam very very quickly as pressure escaped.

it would for that reason be dangerous, and quite the explosive pressure cooker.


--------------------
PEACE

:mushroom2:zippoz:mushroom2:



"in times of widespread chaos and confusion, it has been the duty of more advanced human beings - artists, scientists, clowns, and philosophers - to create order. In such times as ours however, when there is too much order, too much m management, too much programming and control, it becomes the duty of superior men and women and women to fling their favorite monkey wrenches into the machinery. To relieve the repression of the human spirit, they must sow doubt and disruption"

"People do it every day, they talk to themselves ... they see themselves as they'd like to be, they don't have the courage you have, to just run with it."


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OfflineKonnrade
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Re: Pressure and boiling point [Re: TODAY]
    #5942863 - 08/08/06 12:31 AM (17 years, 5 months ago)

Quote:

TODAY said:
Well geewhiz, it's science day at my house!!

I decided I would conduct an experiment today.

Purpose: To determine the relationship between pressure and boiling point.

Method:

1.  Measured two 125mL of water and poured into identical containers and let sit for a few hours to gaurantee that they match room temperature.

2.  Measured the temperature of the room at 32.1 Celsius. 

3.  Poured one of the cups of water into my pressure cooker which has been sitting in the same room and therefore at the same temperature.

4.  Put the pressure cooker, uncovered, on the power burner so that the center of the ring of flames was at the center of the bottom of the pressure cooker.

5.  Turned the power burner on as high as it will go before the ignitor starts clicking (as a benchmark for the next trial).

6.  Timed exactly 360 seconds until all of the water had vaporized.

***Didn't actually do it because I decided it would be too dangerous***

Repeat steps 3-6 but put the lid on the pressure cooker.  When 360 seconds expires (and this is why it is too dangerous) remove the lid of the pressure cooker, exposing the contents of the pressure cooker to the pressure of the room.

I wanted to know if the pressure differential would vaporize all of the water even if it was in a liquid state inside the pressurized container.  I theorize (experimental error being neglected) that all of the water would indeed vaporize.  In theory, am I correct?

:eek:




If the water had all been evenly heated to a temperature greater than the boiling point of water at 1 atmosphere, then yes it would all boil away when pressure was released. The thing is that there needs to be a substantial change in pressure for that to really work, and to gain that much pressure you need a lot more steam than 125mL of water is probably going to create.

And, given all that much more pressure and more water, opening the pressure cooker becomes an impossibility. Firstly because they are usually manufactured so that they cannot be opened when pressurized, and secondly because if you could open it you'd likely sustain greivous and vast burn injuries.


--------------------

I find your lack of faith disturbing


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InvisibleTODAY
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Registered: 09/25/03
Posts: 10,218
Loc: Metropolis City, USA
Re: Pressure and boiling point [Re: Konnrade]
    #5943203 - 08/08/06 03:33 AM (17 years, 5 months ago)

Well, I first considered using 500mL, but I thought that would be alot more dangerous than 125mL. Then I thought that 125mL wouldn't be enough to create a substantial difference than 1atm in the pressure cooker and even that 125mL would be dangerous upon opening...so yeah, that's why I wanted to ask about the theoretical question I asked...because it was impractical to find this out on my own through experimentation.

Sleepy time now zzzz, but Konrade, you did say that my theoretical impression would be correct??


--------------------

ca'rouse (k-rouz)
intr.v.
To engage in boisterous, drunken merrymaking.


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OfflineKonnrade
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Re: Pressure and boiling point [Re: TODAY]
    #5943290 - 08/08/06 05:42 AM (17 years, 5 months ago)

based upon my science nerdliness, I would say that your hypothesis is accurate.

of course, I'm a bit rusty and it's nearly 5AM here... I could easily be forgetting something.


--------------------

I find your lack of faith disturbing


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OfflineSeussA
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Re: Pressure and boiling point [Re: Konnrade]
    #5943336 - 08/08/06 06:55 AM (17 years, 5 months ago)

> I theorize (experimental error being neglected) that all of the water would indeed vaporize. In theory, am I correct?

You could calculate it out, but it is a lot of nasty physics. You are dealing with several different concepts: the idea gas law, phase changes, heat of vaporization, etc.

With a fixed volume, as the temperature increases, the boiling point of the water increases. Eventually, the liquid will become thermally saturated at the greater pressure. (Basically, this means it starts to boil off into water vapor, unable to accept more energy.) If you suddenly reduce the pressure, you also suddenly reduce the boiling point of the liquid. The now excess thermal energy in the liquid will result in a phase change of some of the liquid into vapor. This process will continue until the system balances itself, or until all of the liquid vaporizes.

I would probably work it backwards. Start by figuring out how much energy it takes to vaporize a volume of water at 100C. Next, work out the pressure needed to keep the water in liquid form while holding the energy needed from the previous calculation.


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InvisibleTODAY
Battletoad
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Registered: 09/25/03
Posts: 10,218
Loc: Metropolis City, USA
Re: Pressure and boiling point [Re: Seuss]
    #5943684 - 08/08/06 10:57 AM (17 years, 5 months ago)

Thanks Seuss, I think I've got that calculation of how much energy went in to boil all the water:

100c-32.1c=67.9c and 125mL = 125 grams

67.9c * 125g * (latent heat of fusion = 80 cal/g*DegC) = 679Kcal

+

125g * (latent heat of vaporization = 540 cal/g*DegC) = 67.5Kcal

.................................................= 746.5Kcal

or (1 calorie = 0.00396566683 btu) so... = 2960Btu


I think I've got this right, but not 100%, especially regarding units.


--------------------

ca'rouse (k-rouz)
intr.v.
To engage in boisterous, drunken merrymaking.


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InvisibleTODAY
Battletoad
Male

Registered: 09/25/03
Posts: 10,218
Loc: Metropolis City, USA
Re: Pressure and boiling point [Re: Seuss]
    #5943687 - 08/08/06 10:58 AM (17 years, 5 months ago)

I don't have the necessary formulas to work the pressure part of the equation...damnit!!


--------------------

ca'rouse (k-rouz)
intr.v.
To engage in boisterous, drunken merrymaking.


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OfflineAnnoA
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Re: Pressure and boiling point [Re: TODAY]
    #5946495 - 08/09/06 03:09 AM (17 years, 5 months ago)

You can use the antoin equation to calculate the vapor pressure of liquids:
http://antoine.frostburg.edu/chem/senese/101/liquids/faq/antoine-vapor-pressure.shtml


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InvisibleTODAY
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Re: Pressure and boiling point [Re: Anno]
    #5946868 - 08/09/06 09:39 AM (17 years, 5 months ago)

hmmm, looks like i have some research to do.  or maybe i'll just put my chem friend on it :wink:


--------------------

ca'rouse (k-rouz)
intr.v.
To engage in boisterous, drunken merrymaking.


Edited by TODAY (08/09/06 09:41 AM)


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