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Q: physical properties of water in a vacuum ( Answered ,   3 Comments )
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 Subject: physical properties of water in a vacuum Category: Science > Physics Asked by: halek-ga List Price: \$10.00 Posted: 02 Jun 2002 10:43 PDT Expires: 09 Jun 2002 10:43 PDT Question ID: 20227
 ```A friend asked "how can you lower the boiling point of water so that it is the same as water's freezing point?" How can you make the boiling and freezing points the same? His solution was to place it in a vacuum but he seemed unsure what that would do. What would happen to water in a vacuum? Is there a way to make water's freezing and boiling points the same? It seems to me that that question is equivilant to asking "how can you make 0 degrees the same as 100 degrees?"```
 Subject: Re: physical properties of water in a vacuum Answered By: lazerfx-ga on 02 Jun 2002 11:11 PDT Rated:
 ```Hello Halek-ga. There is a phenomenon in science similar to what you are talking about, the point where the freezing and boiling points of water are in equilibrium. This is called the "triple point" of water. It is where water is a gas, a liquid and a solid at the same time. This is a known scientific phenomenon, and occurs at 273.16° Kelvin, or 0°C. (See references 2 and 3). This is not, however, exactly the same as that possible phenomenon you refer in your question, which is to have water that boils and freezes at the same time. This is possible (see reference 4). Water molecules will constantly leave the water and return - some are lost, and this is why when you leave a cup out for a long time it will loose water. When you lower the pressure exerted on water, you increase the evaporation of the water. When you increase the heat of the water, you increase the energy in the water molecules. At the point when you increase the energy enough, you give the molecules that leave more energy than the surrounding water - this is where the water starts to boil, and we see the bubbles generated by water vapour. Now when you take those two facts and put them together it is apparent that lowering the pressure on the water will cause the boiling point to lower, that is the amount of energy that you need to put into the water before it will boil. Eventually, you can lower that amount of energy to be equal to the point where water freezes - this occurs in a vacuum chamber, and you get frozen boiling water. If you read reference 4, you will find two scientists explanations of this, showing why the water will boil, and how then the water freezes while it is boiling. However, as to your comment on "make 0 degrees the same as 100 degrees" - the temperature as marked on the celcius scale is that of the freezing and boiling points of water at "normal atmospheric pressure", or around 760 barometric millimeteres of pressure (See reference 5). While you change the boiling and freezing points of water when you lower the pressure, you do not change the temperature scale itself. The searches I made: (google) boiling point freezing point identical (1) [ http://www.hii.horiba.com/non/it540/allabout/4.html ] - Interesting facts on temperature (google) Kelvin Temperature (2) [ http://www.unidata.ucar.edu/staff/blynds/tmp.html ] - About Temperature This led to the following link: (3) [ http://www.unidata.ucar.edu/staff/blynds/3pt.html ] - Triple point of water (google) Water boil freeze same time (4) [ http://newton.dep.anl.gov/askasci/chem99/chem99558.htm ] - Ask a scientist, can water boil and freeze at the same time? (google) how celsius is defined (5) [ http://www.cchem.berkeley.edu/ChemResources/temperature.html ] - The conversion of Temperature Units I hope this answers the questions brought up in you and your friends minds. LazerFX-ga```
 halek-ga rated this answer: `very thorough. thank you for teaching as well as answering questions.`

 ```I'd like to elaborate on this. The state that H2O is in depends on both its temperature and pressure. As you lower the pressure of the water, i.e. bring it closer to a vacuum, the boiling point continually drops and the freezing stays relatively the same (it actually increases a minute amount). Eventually the boiling and freezing point meet. This happens approximately at 612 Pa and 0°C. Standard atmospheric pressure is 101,325 Pa, and a vacuum is of course 0 Pa. If you drop the pressure below 612 Pa, then H2O is no longer stable as a liquid and can exist only as ice or steam. This page has a decent phase diagram of water showing this: http://wine1.sb.fsu.edu/chm1045/notes/Forces/Phase/Forces06.htm If you want to get more into it check out this page: http://www.sbu.ac.uk/water/phase.html Here is shown all the various states H2O can occupy including different types of ice.```
 ```I once saw a film of a demonstration of this phenomenon... a pan of water was placed in a large vacuum chamber (run by NASA in the 60s, I think). The air was pumped out. At some point the water began to boil. When water turns to a gas there is a "heat of vaporization" that must be supplied (which is why sweating cools you), in this case by the remaining water. Eventually the water cooled enough to freeze, but it was still boiling! (Which made a really big mess--ice chunks flying everywhere.) Anyway, I have no idea whether this film has been digitized and placed on the Net, or where to find it otherwise (you might try asking the people in charge of freshman physics at a local university), but it is well worth seeing.```
 ```A gross revival of an old topic, I know. How does this property differ from sublimation?```