Weight of C02 in empty keg

[bolts]

Here's my swag at it -- care to check my math?

Reference:

http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

Ideal gas law

pV = nRT

solving for mols
n = pV/RT

n = mol
P = Pa
T = Kelvin
V = m^3


Given a keg (not accounting for exact volume which I supposed is more like 5.25). I have my kegs at 12psi @ 36 degrees -- I like my bubbles.

12 pounds per square inch = 82 737.0875 pascals
5 US gallons = 0.0189270589 cubic meters
R = 8.3145
36 degrees Fahrenheit = 275.372222 kelvin

Solving you get

(82737.0875 * 0.0189270589) / (8.3145 * 275.372222) = 0.68395 mols of C02

C02 weighs 44.010 g/mol

So, an empty tank contains 30.1 extra grams of weight, or 1.06 ounces.

Why you ask? Well, who really needs a reason.

 

[Beerrific]

Here's my swag at it -- care to check my math?

Reference:

http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

Ideal gas law

Oh, there is your mistake right there....lol

 

[bolts]

Oh, there is your mistake right there....lol

Funny thing is ... I have no idea. Just sticking numbers in a formula At least all the units dropped out correctly to mols. Experimentally the results aligns with my experience. I can't tell the difference empty and full of gas or just empty.

 

[RichBenn]

Funny thing is ... I have no idea. Just sticking numbers in a formula At least all the units dropped out correctly to mols. Experimentally the results aligns with my experience. I can't tell the difference empty and full of gas or just empty.

Ah, there's your problem. It's "moles", not mols. (At least when I went to school, which was too long ago to mention:cross

 

[Eisendrath]

Ahhhh Mr. Bolts, Avogadro would be proud of you. Now go have a brew.

 

[soot]

Besides a few cosmetic things (solving for moles is in fact n = PV/RT; your calculations are consistent with it).

What do you mean by empty? Charged but without beer? You're also assuming the tank is charged with 100% CO2.

However, when they we start to discuss deviations from the ideal gas law (ie van Der waals equations; common at high pressures/low temperature).

For a general estimate, you are on point thought. :rockin:

 

[bolts]

Besides a few cosmetic things (solving for moles is in fact n = PV/RT; your calculations are consistent with it).

What do you mean by empty? Charged but without beer? You're also assuming the tank is charged with 100% CO2.

However, when they we start to discuss deviations from the ideal gas law (ie van Der waals equations; common at high pressures/low temperature).

For a general estimate, you are on point thought. :rockin:

Thanks for the feedback -- corrected the typo in the formula.

By empty, I mean as you drain a keg it's fully filling with CO2 at whatever pressure you are dispensing at -- yup, charged w/o beer. Yup -- also assuming the tank is pure CO2.

Glad to see the estimate in the ballpark.