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Does cold air contain more oxygen?


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#1 Argus

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Posted 25 November 2003 - 02:59 PM

Someone told me today that cold air has more oxygen in it.  Is this true?

#2 DLamb

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Posted 25 November 2003 - 03:06 PM

Since warmer air is less dense, I would say yes.

Somebody please correct me if I'm wrong.

[ November 25, 2003: Message edited by: Daniel Lamb ]

#3 Peter

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Posted 25 November 2003 - 03:12 PM

I would say it depends.  From one standpoint, there is more oxygen: colder air is denser, and a given volume (say, one cubic meter) would contain more oxygen, ie. more absolute oxygen molecules.  This is why internal combustion engines work better in cold air (all other things being equal).  But that same dense, cold air also contains more nitrogen molecules and all the other components of air (except for water vapor).  So from that standpoint, the percentage of oxygen in the air doesn't change with temperature.

#4 copasetic

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Posted 25 November 2003 - 04:05 PM

Peter pretty much hit the nail on the head with that one.

Colder air is denser and can hold more of anything introduced to it. Such as Nitrogen, Oxygen, Fuel   Light it. Go fast.

Speaking of look at Nitrous for example. Nitrous is n2o. One part nitrogen, 2 parts oxygen. Its very very cold and dense as the liquid is squeezed out of the tank under pressure. That dense charge of cold oxygen and nitrogen (the nitrogen is just a stabilizer that is seperated from the oxygen during the combustion process)can hold a lot more fuel because the air is dense. Allows you to make more power per cylinder because it can hold more fuel.

To get off my rant.. Colder air just like peter said can hold a lot more of everything.  

Brandon

#5 mcalvert

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Posted 25 November 2003 - 04:26 PM

Yes, there are more oxygen molecules per volume of air as the temperature goes down because the molecules organize themselves closer to a lattice array(solid).  A solid is ALMOST always denser than a liquid and a liquid is always denser than a gas.

Water is the exception to the rule on the liquid to solid density.  Liquid water is denser than solid water.

Temperature is nothing more than a measure of the molecular kinetic energy of an entity.  The more kinetic energy a molecule has, the more space that it requires to maintain the same pressure.  If the kinetic energy of a molecule increases, but the volume in which it is contained doesn't increase proportionally, then pressure increases.

PV = nRT  where P=pressure, V=volume, n=number of moles, R=Boltzmann constant, and T=temperature.

n/V is the molecular density of a given volume of gas, so:

n/V = P/RT.

This states that given constant pressure, as the temperature decreases, the molecular density of the volume increases.



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