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Why couldnt we heat a metal up to 100 deg C by dipping it into boiling water?
In an experiment, our group decided to measure the specific heat of two metals. We did this by heating the metals and putting them into a calorimeter filled with water. To heat the metals, we boiled some water, and then submerged the metals there until they reach their maximum temperature. However, their temperatures were only coming up until about 80 degrees C( this is different for the two metals, which are brass and aluminum). The thing is, the water was already boiling so it was at 100 deg. So my question is how was it that they only reached 80 deg. and just stay there? Were they already at thermal equilibrium or would it just take a long time(like more than half an hour) to do it?
Just to clarify... the boiling water was still over the turned-on stove, when we dipped the metals in them.. when they reached about 80 deg. we put them into a calorimeter. Obviously the temp. of the water rose while the metals cooled.
Back to my question, when we were heating the metals the temperature only rose up to ~80 deg. C. Why was this so? wouldnt it have reached 100 deg. because that was where it would reach thermal equilibrium(right???)...
PS. we measured the temp. of the blocks by slightly lifting them out of the water and then used a thermometer.
PPS. anyways the heat from the stove is continuous so the system's temperature would have had the potential to go higher if it wasnt for water evaporating.. i get that if we added the metals to the water the temp of the mix would be lower, but seeing as heat is added continuously, it would reach back to 100 deg. again.
3 Answers
- Gary HLv 78 years agoFavorite Answer
Not sure what you were doing but there is no reason the metal samples should not have reached the same temperature of the boiling water unless...
If the pieces of metal stuck out of the water or you did not leave them in long enough or they were taking up too much space on the bottom of the pot (in which case they might have gotten hotter than 100C). More likely, there was something about the way you were measuring the temperature of the metal blocks.
Exactly how were you measuring temperature? If you were using a thermometer, the thermometer does not make good contact with a flat metal surface so the thermometer was probably not at the same temperature as the metal. If you pulled the metal out of the boiling water and measured it temp with thermometer, you were getting much more of an air temperature rather than the metal temperature (just like thermometer in water mostly measuring the water temperature).
If you have another piece of metal, drill a hole in it slightly larger than the bulb of the thermometer and, with the block in boiling water, put the thermometer inside the hole. Now you are getting much more of the block temperature and you should see the block warming up all the way to 100C.
In fact, even without the thermometer, if you leave it in long enough and avoid it overheating (because it has too much contact with the bottom of the beaker) the metal can not help but be at 100C. Use a large container of water, you could put small pebbles in the bottom to keep the metal block off the bottom.
- 8 years ago
Is your classroom at 6000Meters elevation? I doubt it.
Put on your 1819 time machine hat and google the definition of specific heat.
How do you measure the metal temperature? Simultaneously with water temperature? Did you turn off the heat? Did the water stop boiling? You didnt say buti think i know the experiment.
You know of course that stuff (like metal or even an egg being hard boiled in a pot) that is more dense than water holds alot more heat than the same amount of water at the same temperature. More stuff to wiggle. So, adding the metal to the calorimeter will cool the water and the object combination and the final temperature will be lower. The amount of heat in the calorimeter is fixed (approximately). The heat is shared by more stuff after adding the block and thus each gets less heat and the temperature shows this new lower level.
The question is... do you know how much lower? You can know EXACTLY if you know the initial temperatures and the amount of each substance in the calorimeter.
If the brass and aluminum blocks were the same size and same room temperature to start then each should pull down the water temperature differently according to their masses.
Make sense.
Hope I'm not off track.
This is a fascinating and enlightening experiment. Remember it when you cook
Say hello to Dulong and Petit for me while your visiting.
- 8 years ago
the energy wouldnt transfer quick enough to heat it up before the water has cooled down...
