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Author: Subject: gas cylinders?
Megamarko94
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gas cylinders?

how can i calculate how much of gas (how many litres) can go in a cylinder at known preasure... for example if preasure is 19bars how many litres of oxygen is in the cylinder.
or any other gas what is the formula that can be used to find out this???

[Edited on 31-7-2011 by Megamarko94]

Oppenheimer
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Look at the ideal gas law:

PV=nRT

P=pressure
V=volume
n=# of moles of gas
R=ideal gas constant
T=absolute temperature

that basically means, PV=(a constant--IF AND ONLY IF TEMPERATURE IS CONSTANT) since R is constant, n is constant (not changing the amount of molecules of gas you have) and T is held constant.

So you can turn that into P1V1=P2V2

Sorry I don't know how to do subscripts

EXAMPLE

P1= Pressure inside cylinder, 19 bars like you said, convert that to atm, 18.75 atm.
V1= Volume of cylinder, let's say 1 L to make it easy.

P2= pressure outside cylinder, 1 atm (the normal pressure we feel just walking around)
V2= volume of gas outside the cylinder (this is the # we want)

Plug in values

(18.75 atm)(1 L)=(V2)(1atm)

Solve for V2 and you get 18.75 Liters of gas.

Megamarko94
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i don"t really get it/
you also need to consider size of the molecule (N2,O2,CO2...)
temperature(if its not constant)
If some one can help with the formula
i realize that the formula is PV=nRT i need volume at known preasure how many (litres or cubic centimetres or any other unit)

Magpie
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PV = nRT

V=nRT/P

R is a constant and is known.

You can't calculate the volume V unless you specify the number of moles n, the absolute temperature T, and the pressure P.

The type of gas does not matter as long as it behaves like an ideal gas, which most all gases do at low pressure and normal temperatures.

Edit:

I have reread your original question and I agree that Oppenheimer's solution is appropriate to this case.

To rephrase your question: What volume of gas is required at room temperature and pressure to fill a cylinder of a given volume at a given pressure?

In this case, since T1 =T2 and n1=n2, the ideal gas law, PV=nRT, reduces to:

P1V1 = P2V2, as Oppenheimer has stated.

Then V1=P2V2/P1

If your case P1 = 1atm. You still must supply the filled cylinder pressure P2, and the cylinder volume V2.

V1 is then the volume of the gas at ambient conditions (room T and P).

Also realize that this is strictly true only for ideal gas behavior. If you run P2 up to 3000psi the gas' behavior will not be strictly ideal. Deviance from ideality will vary with the gas. Published tables for common gases will provide a correction factor to deal with this.

[Edited on 13-8-2011 by Magpie]

[Edited on 13-8-2011 by Magpie]

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Mr. Wizard
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If you know the volume of the cylinder at normal air pressure , then you know how much it holds at normal pressures. If the pressure doubles, then there is twice as much gas in the cylinder, assuming it stays the same temperature. This simplifies the question. If we are talking about tanks of compressed gas such as at a welding supply house, they will have reached normal temperature by the time you see them. They would have been hot as they were filled. If the tank had 1 liter of internal volume, and the pressure was 19 Bar, then there would be 19 liters of O2 in the tank. ( rounding off Bar= 1 atmosphere)

Boyle's Law says when temperatures stay the same, product of pressure times volume stays the same.
P1xV1=P2xV2

This works well for most gasses, but not ones that condense to a liquid, like propane, CO2, freon. It also doesn't work in gasses like acetylene that are dissolved in acetone inside a tank on an inorganic sponge.

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