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Q & A: water condensing from burger

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Most recent answer: 02/01/2017
Q:
If I put a mcdonalds burger in a closed jar and left it there for two weeks and there is water of the sides of the jar. Why would there be water on the jars
- Dedrick Thomas (age 14)
Chicago,Illinois,U.S.A.
A:

This result is a little surprising but not shocking.

Here's why it's surprising. Two weeks should be long enough for the water to reach an equilibrium condition, with the largest possible total entropy of the system and its neighbors. That means the largest possible number of quantum states. In the long run nature seems to be equally likely to land in any state, so what you almost always see is the form that has most of the states.

 The first step would be that the burger, which contains lots of water, will give off water vapor. That's just like how water evaporates from anything very wet, since the molecules in the atmosphere can reach a lot of different states. It seems that so much vapor was released into the air that some of it then condensed onto the sides of the jar. That's surprising because at fixed temperature the water can always lower the net free energy by settling in the regions where there are salt ions, sugar molecules, etc. dissolved in it. That would be in the burger, not on the sides of the jar, where the water is probably almost pure.  

We describe elsewhere (http://van.physics.illinois.edu/qa/listing.php?id=31313) why the water goes where things are dissolved in it. The fundamental reason is that by doing so it allows those dissolved ions and molecules to run around in a larger volume, increasing the total number of states that the system can be in. So in equilibrium that water should be back in the burger or the bun, not sitting in pure form on the glass.

Here's my guess as to what happened. The burger was probably hot to begin with, which causes a lot of water to evaporate. The jar was colder, so some of the vapor condensed out onto the jar. 

Over a long period of time at fixed temperature, the water should go back into the burger and bun. Over that long a period you could get other changes too, such as bacteria digesting parts of the burger.

Mike W.


(published on 02/01/2017)

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