the air we breath

[Helius]

Hello ppl,
I'm new here, been diving for a year and like that very much.

I have a question, something I have thought about latly...

WE breath air which was compressed into a tank. Now as far as I know, when we compress a gas over 4-5 atm. it doesn't act as a regular gas (called 'ideal' gas). Moreover, at 200 atm. it should turn into liquid, yet it's still in the form of a gas.

So, anyone ever thought about that, or know why it's still a gas?

=-)

 

[Stone]

"Gases must be subjected to very low temperatures in order to become liquids. . . (as a general rule, the volume of a given sample of gas decreases by a factor of about 800 when it forms a liquid)".

 

[Helius]

yeah, I guess you are right.

10x.

 

[pescador775]

It depends on the gas. I guess that quote came from some dive pub, it figures. Some common gases become liquid at pressure and at room temperature. Examples are propane and carbon dioxide. The atomic forces associated with the gaseous elements of air prevent liquifaction under these conditions.
Pesky

 

[Helius]

WEll, I'v looked into some books and I think it has to do with something that's called 'the triple point'. It's a graph of condiotions at which the gases change from solid to liquid to gas or solid to gas etc. ( forgot the word for that))
Anyway, as far as I know, each one of the diffrent gases that we breath has a different triple point, which mean it can be found at the liquid stage, gas etc. under different conditions (temprature and pressure).
As pescador775 said, the known example is the carbon dioxide that only under 5atm and -57 C we will find the liquid form.

I don't think that the atomic forces are the reason, BUt I'm not sure of that. If I think about that, 200 bars are a lot of pressure and we can see some gases as liquid at a lower pressure....


I hope it's not too messy...
=-)

 

[Goldminer]

Helius once bubbled...
Hello ppl,
I'm new here, been diving for a year and like that very much.

I have a question, something I have thought about latly...

WE breath air which was compressed into a tank. Now as far as I know, when we compress a gas over 4-5 atm. it doesn't act as a regular gas (called 'ideal' gas). Moreover, at 200 atm. it should turn into liquid, yet it's still in the form of a gas.

So, anyone ever thought about that, or know why it's still a gas?

=-)

The forces that result in non-ideal behaviour of gases are called Van der Waal's forces. If thermodynamics does not bore/confuse the s**t out of you do a google search on the term. You will get a lot of info. Ideal gas behaviour is a relationship between pressure volme and temperature of gases described by the formula PV = nRT (may have got the caps wrong here).

No gas is an ideal gas though and they get further away from ideality as pressure increases. For this reason it takes a different amount of air to put the first 100 psi into your tank than the last 100 psi when it is full. In other words if you drop from say 3500 psi to 3000 psi you have not lost 1/7 of the tank's air. If you look at OMS's website you will see that their claimed volumes are van der waals adjusted.

As for liquification this is related but is a function of temperature and pressure. At room temperature I do not beleive that air will liquify at the pressures you gave. It can liquify at room temperature if the temp is low enough.

 

[Caffiend]

Helius once bubbled...
or solid to gas etc. ( forgot the word for that)

That's sublimation.

-will

 

[sheck33]

Helius once bubbled...
WEll, I'v looked into some books and I think it has to do with something that's called 'the triple point'. It's a graph of condiotions at which the gases change from solid to liquid to gas or solid to gas etc. ( forgot the word for that))
Anyway, as far as I know, each one of the diffrent gases that we breath has a different triple point, which mean it can be found at the liquid stage, gas etc. under different conditions (temprature and pressure).
As pescador775 said, the known example is the carbon dioxide that only under 5atm and -57 C we will find the liquid form.

I don't think that the atomic forces are the reason, BUt I'm not sure of that. If I think about that, 200 bars are a lot of pressure and we can see some gases as liquid at a lower pressure....


I hope it's not too messy...
=-)

The triple point of gasses or metals is that set of conditions, temperature & pressure, where the gas/metal can have all three fases, gas, liquid, solid, present at the same time.

triple points are actually used as temperature references because they are extremely well defined temperatures at a given pressure.