454073 Thu Oct 25 11:17:33 -0700 2007 15 29 Not About Food 0 3066769 I had a tupperware of chicken soup in the freezer. On Tuesday morning, I decided I would like to use it for dinner that night. I don't have a microwave, so I pulled it from the freezer, put some very hot water from the tap in a metal pot just a bit bigger than the bowl, put the bowl in the pot, and put the pot in the fridge. My idea was that the hot water would melt just the outside of the contents of the bowl before it cooled off entirely, so I could get the soup out and gently melt/heat in on the stove later. I came home to find the bowl surrounded with ice. It was so strange. The water was 140 degrees (I've checked the temp of the hot water in the apartment), and the fridge was normal fridge temperature. Nothing else was frozen - no frosty milk, no back-of-the-fridge frozen vegetables. So how on earth did the frozen bowl freeze the water around it? When you put an ice cube in cold water, it never freezes the water. But I admit to being a bit slow when it comes to basic science - can someone help me out? Thu Oct 25 11:17:33 -0700 2007 12806 curiousbaker 1 3066874 I'm not a scientist, but it seems to me that if the contents of your Tupperware were pure ice (i.e. nothing but water), it would be 32 degrees and the surrounding water would likely not have frozen. But the various ingredients in your soup mean you're no longer dealing with pure water, your soup has a freezing point well below 32 degrees. Salt alone will drop the freezing point of water a few degrees (hence why it's put on roads in icy conditions). Who knows what chicken, carrots, celery and a little schmaltz will also do??? Surround that sub-32 degree frozen block of soup filling the Tupperware in contact with water that has cooled off quickly in the refrigerator, and suddenly some of the surrounding water is brought down to 32 degrees, or ice, while your block of soup is melting very slowly. Thu Oct 25 11:40:33 -0700 2007 3066769 12051 tubman 1 3066898 Although you fridge temp is normal, I suspect that your freezer temp is much lower than normal. You chicken soup must have been very very cold (much below freezing). Hence, the coldness from the soup was enough to freeze your water. If you put really cold ice into a glass and sometimes, a layer of frost will develop on the outside. This is because the ice is cooling the water vapors surrounding the glass and freezing it. Thu Oct 25 11:47:04 -0700 2007 3066769 26785 elainew 2 3066924 Most home freezers should be set to about 0 F - which is 32 degrees F cooler than the freezing point of water - so the answers above are right to my knowlege, but the freezer temperature is probably actually about where it should be. Thu Oct 25 11:53:33 -0700 2007 3066898 27702 LauraB 1 3068993 It’s a matter of mass and energy transfer. The fridge is ~40 deg/f. You put a metal pot, which is a good conductor, in the fridge. Inside the pot was a relatively large quantity of ice (sub 32 deg/f) and a small quantity of hot water (probably ~120 deg/f). In a closed system, if you had, say, 6 cups of ice and 1 cup of hot water, at equilibrium, assuming the temps I cite above, their average temp would arrive at 44.5 deg/f (not too far above freezing as it is). This was not a closed system in that you have the fridge actively working to continue cooling the pot; you know the fridge will win out in the end and the ultimate temp will be around 40 deg/f. Whether you put a lid on the pot or not doesn’t matter, as long as it was in an unopened fridge, it would create a cold air sump, essentially a mini cooler inside a bigger one. Both the pot and the ice block drew heat from the water/transferred “coolness” to it. The small volume of water relative to the mass of ice/pot and surface area would have quickly cooled (it was probably barely even warm when it went into the fridge). Because metal is a better conductor than a block of ice, that heat quickly radiated into the fridge, thereby doing little to raise the temp of the ice. Then, since the pot created a cool spot, and it was already in a cold environment with little temperature differential between the air outside the pot and inside it, the block of ice continued to chill the smaller volume of water, with the pot acting as an insulator and only gradual heat loss to the external environment. Your idea probably worked, you just got back to it at the wrong time. The hot water probably did melt the soup enough for it to slide out of the container. However, it did so, within the first few minutes of contact. After that, the energy transfer briefly described above took place. Of course, had you waited a while longer, the whole thing would have begun to melt again, and it would have slipped right out of the Tupperware. Fri Oct 26 06:35:12 -0700 2007 3066769 12583 mark 2 3073011 Mr. Mark: That is a ok explanation of over all what is going on, but some of the details are not quite right. Now this isnt a physics forum so we dont need to worry about second order effects, but this is still far enough off to merit some explanation ... i.e. correct to first order approx is good enough but the above is more like correct to half and order approx. The main problem with your calculation above is it does not account for the very significant "phase change tax" which you must pay to take ice at 32degF to water at 32degF [the fancy term for this "melting tax" is "heat of fusion" and it is about 80cal/gm of water]. So let's re-cast your example as "you have 6grams of ice at 32degF and you add 1gm of water at 120degF, what is the final temp?" [we dont want to use "cups" because that is a volume measure and ice is less dense than water]. 120 degG =~ 50degC so you are adding about 50 calories [1gm * 50 deg] ... since the heat of formation of you ice block is 80 * 6 = 480 cal, that little bit of hot water wont even melt all the ice, let alone get you to 44.5 deg. Since this is so far short of the heat of formation, at a macro or observational level we can confidently say what you will be left with will still be at 32deg. To the OP: just a couple of things: 1. heat "moves" in one of three ways: radiation [invisble rays of heat radiating off a surface], conduction [touch] and convection. your's is a conduction dominated case, and donesnt involve mass transfer. just energy transfer. 2. it is useful to understand the difference between heat and temperature. heat is a mesure of the actual energy in the object. different materials take a different amount of energy to raise a fixed mass by one degree. somewhat counter intuitively [since we often think in terms of volume] it is harder to raise the temp of 1kg of water by 1degree C [that takes one kilo calorie ... which is the calorie on you food package] than to raise the temp of 1kg of iron by one degree ... water takes about 9x as much energy per unit *mass*. but since iron is about 8 times denser than water, per volume, it's about the same amount of energy to heat a 10cm x 10cm x 10cm block of iron weighing about 17.5 lbs by one degree as it is to increase the temp of a litre of water by one degree. [formal term = heat capacity]. Anyway, the way to do the equillibrium analysis is to figure out the input energies if each of the input components and then the constrain is at the end of the process the whole system must be at the same temp. Anyway, to leave the realm to theory for practice, I suspect what you want to do is either just put the container of soup in the fridge with no water bath before you go to work, or ... what i would probably do ... is to put the sealed container or soup in a *large* hot water bath in the sink *and keep refilling it with hot water as the ice block soup cools down the ice water bath* ... this way you have both conductive and convective heating. also the rate of heat xfer is proportion to the temperature difference [but this gets complicated]. this is sort of the theory behind an champagne ice bucket. if you want to cool a bottle fast, dont fill your ice bucket with ice, but with as much ice as you can fit in and then add water. and then add more ice as the ice melts. Sat Oct 27 16:31:24 -0700 2007 3068993 16770 psb 3 3091130 psb and Mark, Was the Mpemba effect at all a factor? --That in certain common situations hot water freezes more quickly than cold water. Your thoughts, please. Certain conditions that support Mpemba are here http://www.school-for-champions.com/science/mpemba.htm Fri Nov 02 21:21:09 -0700 2007 3073011 18222 maria lorraine 4 3091167 mark posted a v. good explantation....Mpemba has more to do with experimental design and experimental error.... Fri Nov 02 21:40:28 -0700 2007 3091130 19117 Pollo 5 3091277 I am happy to accept Mark's explanation, but I'd like to hear more. I've been curious about Mpemba awhile. Are the factors in curiousbaker's situation the same as those usually found in Mpemba re: conduction, evaporation, convection and dissolved gases? I don't know if Mpemba occurred in this situation, but the scientific articles below indicate Mpemba is real and a fairly reproducible phenomenon: Links: Investigating the 'Mpemba Effect': Can Hot Water Freeze Faster than Cold Water? http://www.sciencebuddies.org/mentoring/project_ideas/Phys_p032.shtml Monwhea Jeng's "essential reading" on the topic, written awhile getting his Ph.D. in Physcis at UC-Santa Barbara: Can hot water freeze faster than cold water? http://www.physics.adelaide.edu.au/%7Edkoks/Faq/General/hot_water.html Scientific American, Walker, J. 1977. "The Amateur Scientist: Hot Water Freezes Faster Than Cold Water. Why Does It Do So?" "Does Hot Water Freeze First?" Physics World http://physicsweb.org/articles/world/19/4/4. "Hot Water Freezing" Hyper Physics http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/freezhot.html#c1. Investigating the 'Mpemba Effect': Can Hot Water Freeze Faster than Cold Water? http://www.school-for-champions.com/science/mpemba.htm Fri Nov 02 23:36:39 -0700 2007 3091167 18222 maria lorraine 6 3096188 There may be some corner cases in the phase/energy analysis, but the lesson is NOT "if you want ice cubes quickly, run the tap till you get hot water coming out". [i suspect there may be some initial configurations with very high surface area where this might be the case. i seem to remember watching some food show where they were making granita by freezing a couple of milimeters of dairy on a flat plane ... that's the kind of corner case I was talking about. again i dont know anything about cooking, so i might be off here.] A basic understanding of conduction/convenction/radiation, the parition of energy and a little intuition should be reliable guide in pretty much all real world cases ... you dont need to read Landau and Lifshitz to know why agitating/pouring a liquid makes it cool faster. There's also the somewhat famous example of "if you want your coffee to be as hot as possible in 10min, should you add the cream now, after 5min, or just before you are going to drink it". Dont most people know intuitively [caeteris paribus] hot things cool faster than cold things? you dont need the stefan-boltzman law and partial differential equaitions to tell you at add the cream now. [BTW, there are some counter-intuitive things in the area of convective cooling and laminar and turbulent flow, but that is beyond the scope of this posting. Conduction is usually simpler. ok tnx.] Mon Nov 05 09:02:18 -0800 2007 3091277 16770 psb 1 3092586 i'm still confused as to why the op put a pot of hot water in the fridge. did you think it would stay hot? without getting all science geeky, if you just took the container out of the freezer and put it in the fridge, by itself, it would have thawed normally and safely. instead you essentially put a protected block of ice in water in a conductive container, in a very cold environmnet. Sat Nov 03 15:49:52 -0700 2007 3066769 30273 hotoynoodle 2 3096420 No, I didn't think it would stay hot. I've just had the experience of putting things in the fridge out of my deep freeze and coming home to find them completely unchanged. No melting, none. So I thought that the hot water would melt it just a little bit on the outside, and then it would just become cold water, and the container would sit in it, ever so slightly melted on the outside, still frozen on the inside. But, clearly, that was, um, wrong. Not much of a science geek, I'm afraid. To the poster who asked if it wasn't intuitive to add cream to coffee now rather than later, I have to say no. In no way is that intuitive to me. Sorry. (That something very hot will cool off at a faster rate than something already cold, sure. But not what that has to do with when you would add the cream.) But at least I'm better off than an ex-boyfriend who didn't understand that covering a cup of tea would keep it hot longer. That should really have been intuitive, but it wasn't, not to him. He was a poet, which may excuse him. Mon Nov 05 09:51:31 -0800 2007 3092586 12806 curiousbaker 3 3097522 Hmm, this is interesting. I guess I should have added [i thought i'd said this before] a lot of people's intuition fails because they dont distinguish between HEAT and TEMPERATURE. "regular people" probably reasonably think in terms in terms of temperature being the essential property of an object. this is understandable since that's what we focus on when we set the thermostat, the oven dial or read the weather report. i guess there is a sense that heat is "what comes out of a heater", or is "given off" by a hot object, rather than being a property of a physical system. in addition to the greater familiarity with temperature, maybe there is a linguistic element adding to the confustion. we all agree that a glass of cold milk has a temperature, but "regular people" may not think of it has "having heat" ... if anything, they think cold is "not heat". but heat, like mass, is a fundamental property, not an editorial one ["hot" is "editorial"]. we can say cannonball is "heavy" [editorial] but it is also perfectly reasonable to ask "how heavy is this feather" [non-editorial]. This is kinda ironic because scientifically temperature is a much harder thing to define. ok tnx. p.s. i think it's fascinating to meet people with no intuition or knowledge about science. i live in bay area and it's "common knowledge" here the golden gate [meaning the gap between san francisco bay and the pacific] affects the weather here. an associate of mine who was a writer somehow turned this into "the golden gate *bridge* affects the weather". you can tell them all kinds of crazy things and they'll believe it because they have no ability to do a "reality check". we then told my associate the color of the paint on the GGBridge is how it affected the weather. i guess he remembered there was something "special" about the color of the bridge, so this resonated in his mind and he accepted the explanation. more appropos to CH, apparently a a lot of people will "swear" putting a (siilver?) spoon in the neck of a champagne bottle will keep it fizzy? that is crazy. no PDEs needed. Mon Nov 05 13:55:16 -0800 2007 3096420 16770 psb 2 3097622 I don't understand this either: why would this be easier than simply taking the container out of the freezer, submerging it in hot water for a minute or two until the edges melt slightly, then dumping into another container on the stove for heating? It seems to me that it would be just as quick: melting the edges enough to release the food wouldn't take that long. It also seems that putting that much hot water in the fridge would raise the temperature of the food around it and put that food in the "danger zone." Mon Nov 05 14:17:57 -0800 2007 3092586 57415 rubinow 1 3095867 My guess is that your pan of hot water didn't hold enough hot water for the job once the container of soup did its displacement thing. A far more effective method would have been to just sit the tub of soup on the countertop while you went to work. Assuming it was at least a quart container, it would still have been cold when you got home after an 8 hour day. More than a quart and you could have still had a blob of ice in the middle! Mon Nov 05 07:45:38 -0800 2007 3066769 112096 Caroline1 1 3097586 ER, your chicken soup ice cube was bigger than your water? Mon Nov 05 14:10:59 -0800 2007 3066769 61669 Quine