"Elaine T" wrote in message
. ..
spiral_72 wrote:
1 LITTLE PERCENT!!!???!!! WHAT'S UP WITH THAT?

Actually, the ONLY thing I am concerned about is I throw the ice in
this dude....cork it..... have it build up pressure and the CO2 only
lasts five minutes. I have no idea what the equivalent gas volume a 1
pound chunk of dry ice has.


Well, the volume depends on the temperature but the ideal gas law lets
you calculate it. (more or less)

pv=nrt
p = pressure in atmosphteres
v = volume in litres
n = number of moles
r = a constant = 0.08205 L atm / (mol·K)
t = temperature in degrees K.

C02 is 44 g/mol and a pound is 454 grams so you have about 10 moles of
C02. At standard temperature and pressure (273K or 0C and 1 atm), one
mole of gas is 22.4 L of volume. So your 1 lb block would sublime to
occupy 231 litres of volume at freezing.

You can use the number of moles, your tank volume, the temps in the
tank, and this equation to predict the actual pressure in your tank in
atmospheres.

....and you've already provided the volume and pressure, so he can just solve
for the new pressure after finding out his cylinder volume. P1V1 = P2V2 as
you know, so

(1 atm)(231 litres) = P2(cylinder volume). This is the pressure at 0C.
Spiral - just divide each side by the temperature (T1 = 273 and T2 = room
temp or whatever you want) and solve for P2 if you want to know your
pressure at different temperatures. You might need to look at a property
diagram for CO2 to make sure your results are correct. If you calculate
your pressures to be too high, for example, you might be getting a phase
change in reality.

dwhite