|MadSci Network: Chemistry|
David, thanks for your question. Freezing a room full of water is an interesting thought. I don't see any reason why you could not freeze water with liquid nitrogen. I did a couple of quick "back of the envelope" calculations to see how reasonable it would be. You said in the question that the room was 10 feet cubed. That means there is 1000 cubic feet of water. By making a couple of assumptions, I calculated the amount of liquid nitrogen necessary to freeze your room of water to be about 6000 pounds (3 tons). That is a very large canister of liquid nitrogen. A concern with your hero using that much liquid nitrogen is that after all of the nitrogen evaporates, there may not be enough oxygen left for him to breath. Freezing this much water will require the removal of a tremendous amount of heat, which makes it somewhat difficult. Another idea for cooling and possibly freezing the water would be to use the same principles that are used for the instant cold packs that athletic trainers use to treat injuries. In these packs, a simple endothermic chemical reaction occurs that removes heat from the liquid. (Endothermic reactions require heat, while exothermic reactions give off heat during the reaction.) Several chemicals that have been reported to work for these applications are sodium acetate, ammonium chloride, sodium nitrate, sodium thiosulfate, potassium iodide, calcium chloride, and ammonium nitrate. All of these are supposed to work with water. (I found these in US patent #3977202, issued to Johnson & Johnson, New Brunswick, NJ.) Some of the chemicals are pretty common: calcium chloride is used as ice melt and ammonium chloride is a fertilizer. I don't know how rigorous you want to be with this topic, but I should warn you that there are potential mixing problems that will arise during the reaction that would stop the reaction. If enough salt is added to freeze water, the water closest to the salt will freeze, effectively creating a protective layer around the salt and stopping any further reaction. If the system was well mixed, this problem could be reduced. I hope I have helped with your novel. It may simply require a little literary license to freeze the room of water.
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