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Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: danielle on March 27, 2004, 02:50:27 PM

Title: thermodynamics (Boiling by splashing cold water)
Post by: danielle on March 27, 2004, 02:50:27 PM

when you place a bottle of water under a flame, wh y when boil it, then put a cork on it and then splash it with cold or room temperature water it keeps on boiling??? ???

Title: Re:thermodynamics
Post by: Mitch on March 28, 2004, 02:16:30 AM

Because the pressure is lower in the bottle which make it boil easier.

Title: Re:thermodynamics
Post by: gregpawin on March 28, 2004, 03:22:05 AM

Right, by the sounds of it, the steam has pushed out all the other gases in the bottle and when corked, contains just steam.  If you cool the steam, you decrease the pressure by condensing the steam into water, lowering the pressure and boiling point.  If you put a little water in a soda can, boil it over the stove and turn it upside down in a bowl of cold water, the pressure will decrease in the can that only has steam in it and the atmospheric pressure will crush the can.

Title: Re:thermodynamics
Post by: GCT on March 28, 2004, 03:00:55 PM

Here's an easy way to think of it.  A liquid boils when as a result of expansion against its atmosphere.  When you close the bottle, the pressure inside the bottle is higher than 1 atm and thus expansion ceases.  When you cool the bottle, the temperature of the vapor decreases faster than the liquid phase (you should look at a phase diagram to see this), the pressure decreases. However, due to the kinetic energy already present in the liquid portion...the liquid is able to expand further once more and thus boils.