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Author Topic: Does the pressure inside a sealed glass jar change over time?  (Read 2827 times)

Offline taregg

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if you have empty jar glass closed for long time  and temperature keeping  changing from cold to hot out side. so what will hapen to thr pressure inside the jar . does it  dicrease or increase actually.

Mod edit: Please phrase post titles as questions.
« Last Edit: 05/03/2013 15:33:47 by JP »


 

Offline CliffordK

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Re: i have test question
« Reply #1 on: 04/03/2013 20:53:23 »
If the jar has a good seal, and the contents are not chemically or biologically changing, then the overall pressure would remain unchanged with the same temperatures. 

I.E.  heating it will generally increase the pressure, cooling it will generally decrease the pressure. 

There are a few cases of negative thermal expansion.

For example, if you had the jar full of water, and decreased the temperature from 4C to 1C, the pressure may in fact increase (not considering freezing).

Now, consider if you had a leaky seal.
Heating your jar, you may increase the pressure slightly before the seal starts leaking, but it may or may not quite equilibriate with ambient pressure.  Then you may loose contents from the jar (air?). 

When you cool the jar again, it may form a seal, and give you a negative pressure inside the jar, which it may be able to maintain.  Or it may leak back to ambient pressures.

At some point, repeated heat/cold cycles would not further change the contents/pressures.

Some substances with high vapor pressures such as gasoline may slowly boil out of the can during the heat, then form a seal in the cold, and partly collapse the can.

Some people recommend flipping canning jars upside down during the sealing process (after you've squeezed the air out with heat) as the liquid against the lid may improve the seal.
 

Offline taregg

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l mean with out sealing . the supervisor of the site he edit the question and add the word sealed..
 

Offline yor_on

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Hot means more pressure as you agitate particles, think of heating water becoming steam, but in a open container that pressure mix with the normal atmospheric pressure, so to notice it you either need a he* of a big (open) water boiler, half the planet preferably, or you put a seal on it and then the pressure definitely raise inside it. Interacting with the atmosphere solely it adapts to that, so when it is hot it should be slightly more pressure acting on the water than when cold as I think. We have stuff reacting on pressure at home, barometers, that sense that pressure by some spring mechanism or other way, think you can use some sort of grass (hay?) too, to see? I'm sure someone here knows what I'm thinking of :)
« Last Edit: 05/03/2013 17:42:32 by yor_on »
 

Offline Pmb

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if you have empty jar glass closed for long time  and temperature keeping  changing from cold to hot out side. so what will hapen to thr pressure inside the jar . does it  dicrease or increase actually.

Mod edit: Please phrase post titles as questions.
Glass and metal have different coefficients of expansion which means that the seal will change with temperature. This could possible leak glass depending on how the glass container is sealed. I also believe that some metals will absorb gas so that the number of molecules in the container will decrease thereby reducing the pressure a very tiny amount. I used to work at MKS Instruments and I recall something like this in pressure sensors.
« Last Edit: 06/03/2013 00:25:29 by Pmb »
 

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