Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!security!genrad!decvax!harpo!seismo!hao!hplabs!sri-unix!KING@KESTREL From: KING%KESTREL@sri-unix.UUCP Newsgroups: net.physics Subject: sudden freezing of soda when cover is removed Message-ID: <15017@sri-arpa.UUCP> Date: Tue, 3-Jan-84 11:57:00 EST Article-I.D.: sri-arpa.15017 Posted: Tue Jan 3 11:57:00 1984 Date-Received: Thu, 5-Jan-84 01:39:00 EST Lines: 45 From: Richard M. King I can think of a few reasons why soda should suddenly freeze when the cover is removed. I will list them in what I judge to be the order of importance. 1> A solvent's freezing point is lowered in direct proportion to the amount of solute. This is a large effect which is used to protect car radiators at temperatures of -40 or less. When the cap is removed the CO2 bubbles out, leaving behind a more dilute solution that suddenly finds itself below the freezing point. 2> Dissolution of an acid-forming solute is exothermic; therefore "precipitation" of that solute would be endothermic. (Anybody remember the fancy term for a gas bubbling out of solution?) The soda froze because it got colder. 3> Pressure is a factor, but a minor one. I seem to remember that pressure changes the freezing point by less than .1 C per atmopsphere. (Isn't the triple point of water 0.015 C at some very low pressure?) If you had tried to go ice skating on that day, where your blade would put your (say) 150lb weight on a blade (say) 1/16 in by 8 in for a pressure of 200 atmospheres, you wouldn't have gotten very far. Even that very high pressure couldn't melt ice below about -15 C (5 F). (I concede that this last "measurement" was made when I was a kid, say 100lb, but even this "modest" pressure of 130 atm. is MUUCCCHHHH higher than that of a soda bottle. (Do not protest that skate blades are thicker than 1/16 in. They are deliberately "hollow ground" as shown below to make the area of contact small. | | |<---------- 1/8 - 3/16 in ---------------->| | _____________________ | | __------ ^ ------___ | | / | \ | | / .04in or so \ | |/ ..............V. \| The depth and curvature of the hollow grinding have been exaggerated by the primitive nature of the "graphics". Dick -------