Hello all, lay-man's question about gas laws

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  • Thread starter Oobray
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Hello all, I have perused this forum for a while now. I've never signed up because I have nothing to offer you folks. I'm not evan an amateur, I'm just interested in physics. I'm a critical care / flight medic, so my understanding of physics is really, really, really limited. Although, I'm highly interested and constantly read and study, and observe. Gas laws area actually something I think about on a pretty regular basis (02 / CO2 diffusion, gas expansion at altitude etc.) However, I observed something today that no amount of googling has given me the answer to. So here it goes....

I am visiting my grandmother who hoards food like no one else I know. She puts everything in the freezer, including her potato chips. In this case it is specifically Ruffles Original potato chips. She placed a NEW unopened bag in the freezer. The bag was normal volume (she lives at about 500 ft elevation) when she put the bag in the freezer. When I went to take it out today the bag looks as if you took it up to 15,000 ft. I have wracked my meager mind about what little I know of gas laws to try and figure this out, but I can't. Everything I know says that gas volume compresses at lower temperature, not expand. What's even more perplexing to me is that it's a PERMANENT change. Meaning, hours after having the unopened bag out of the freezer, it still looks like it's about to burst.

I also wondered if it was something more to do with the bag, however, I don't have an unfrozen bag to compare to. I know, this is probably really elementary but I didn't know where else to turn to. Take it easy on me :)

Thanks!
 

Answers and Replies

  • #2
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It's not surprising that if a sealed soft container including gases is put in to a fridge it will shrink.
Taken out of the fridge it should eventually resume a slightly pressurised condition exactly as it was before being frozen.
It depends a on what the gas is though, but I doubt that Ruffles chips are packaged with hydrogen.
 
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Yes, it's much more than "slightly pressurized". It's about to burst. And it's not just this one, my grandmother says all potato chips do this in the freezer, not fridge.
 
  • #4
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Well in principal additional gas could result from food decomposing, but of course the whole idea of freezing it is so it won't do that.
OK, this one has me stumped, anyone else?
 
  • #5
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That makes me feel a little better. I'm wondering if it has something to do with the material of the bag. Over last few days I put some more chips on there and they're already bloated, except for the tortilla chips. Which of course appear to be in a different material bag. Next step will be to get another bag of chips and see if I can compare them to see if the bag shrunk. Kind of a silly thing to occupy my time with, but I just couldn't figure it out.
 
  • #6
nasu
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The phenomenon is reported in several places on the web, either with chocolate chips or even with zip bags. However I don't have and did not find a reason for it.
Maybe we need to experiment and investigate this phenomenon. :smile:
 
  • #7
sophiecentaur
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If there is organic matter in a sealed bag, it's always possible that some living organism is producing gases during respiration. Tins (/cans) of food can 'blow' in the same way. There is no gas-law reason why reducing the temperature would increase the pressure.
 

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