Math help? How much pressure of x amount of co2 in y volume?

Need some math help folks.

Trying to determine the pressure of 300g of CO2 in a 6L vessel at 100c.

Eternally grateful for any help anyone could offer.

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sure

the ideal gas law is as follows:
PV = nRT, where P = pressure, V = volume, n = number of moles of gas, R is a gas constant, and T is temperature in Kelvin.

given variables: V = 6 liters, n can be calculated from the grams of co2 given (mw of co2 is 44g/mol, so 300g of co2 is 6.82 moles), R comes from a database, it can change depending on what units you are working with, so be mindful, in this case will be 8.31e-2 Lbar/Kmol, and temperature is in Kelvin. and of course you are solving for p.

so P(6L) = (6.82mol)(8.31e-2Lbar/Kmol)(373K)
solve the equation to yield 35.2 bar

hows that sit?

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Awesome, thank you so much!

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my pleasure

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thanks @YeahBet

there are of course web based calculators too.

Ideal Gas Law Calculator | Calistry

requires knowing how many moles you’re using, which requires the molecular weight of the substance in question.

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Extending for folks that came here for decarb.

1mol of THCA (~358g) will produce 1mol of CO2 upon decarb.

the math done by @YeahBet can be rearranged to show that 358g THCA in a 6liter container at 100c would produce 35bar x 1mol/6.8mol => 5.1bar => ~75psi

putting 358g THCA in a 1liter jar would give closer to 450PSI (if canning jars were up for that sort of nonsense).

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Howdy @cyclopath do you mind clarifying something for me?

If I was going to decarb a batch of 2,000 g of THCa (assuming 100% for math’s sake) in a 6L vessel at 100C

2000 g (THCa) = 5.59 mol THCa

P(6L) = 5.59 mol (8.31e-2Lbar/Kmol)(373K)
P=28.87 bar

would I then take 28.87 bar and then multiply this by 1mol/6.8 mols to determine expected pressure within my vessel? I do not quite follow why this was done on your behalf.

istockphoto-1305308408-640x640

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No.

That was to take pressure calculated for 6.8mols of CO2 in a 6L container and trivially recalculate for 1mol(of thca)

Why?

Because I’m an idiot and thought it would help….

You should go look at another example actually tailored to the task at hand.

And don’t forget that 2kg of thca takes volume.

You’ve got 1.8-2less liters for the CO2 to be with that thc…

Iirc the math is here: A Theory on BHO/Rosin Decarboxylation with Natural Terpene Preservation

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yea 28.87 bar is like 420 psi lol

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They obviously had us in mind when making that unit of measurement!

thanks @cyclopath I will be digging into this thread. I appreciate you

Yep, but with only 4l of headspace…

300g = 6.817mol CO2

511.258677 PSI

@woodwardbdb

So you could absolutely multiply it by 6/4 (volume) and 5.59/6.8 (mols) to come up with

35.2bar x 1.5 x 0.82 ==> 43bar.

(wrapping your head around why that works might help…but don’t sweat it. Just use the online calc)

Then double check that with one of the online calculator’s…

image

Thanks for the link @DrWHY420; here’s todays math…

If you’re actually decarbing 100% THCA, performing it under vac makes more sense.

If you’re decarbing 80-90% thca, and want to keep pressures down, to avoid venting of your prv, you need more headspace.

Ok let me try this again…

If I am going to decarb a batch of 2,000 g of THCa (assuming 100% for math’s sake) in a 6 L vessel at 100C

2000 g (THCa) x 12.3% = 246 g CO2

246 g (CO2) = 5.59 mol

Due to headspace although I am in a 6L vessel assume volume of 4L

P(4L) = 5.59 mol(8.31e-2Lbar/Kmol)373K
P= 43.31 bar or 628.15 psi

So if I am mathing correctly that is way to much material for a 6L vessel.

So in reality the equation I should be performing is finding for mol of CO2 not P

Target pressure 8 bar / 115 psi

If I change batch size to 500g opposed to 2,000 g

500g (THCa) x 12.3% = 61.5 g CO2

61.5 g (CO2) = 1.4 mol

P(5.5L)= 1.4mol(0.0831Lbar/Kmol)373K
P= 7.89 bar or 114 psi

This seems like a much safer volume of THCa to decarb in a closed vessel

[grammar]

Why would you want that though. Id assume the pressure of the byproduct /product will slow the reaction over time

reaching 115 psi would indicate full decarboxylation of THCa in this hypothetical scenario. In theory you could utilize the pressure gauge to determine % conversion of THCa to THC

decarb is pretty efficient, and even if one were to miss a few percents, if one is distilling afterward, even a 90-95% efficiency wouldn’t matter because the terp strip/distillation will certainly get the rest.

I decarboxylated under vacuum, as others have suggested, because pressure is not friendly, in my chemistry mind, you always want to remove reaction by-products as they are formed to influence the forward reaction (not sure if Le Chaltier’s applies here or not), and a stable surface interface of the crude oil is a pretty good indication that decarb has ended.

I wonder if a heat/mass test would be appropriate here. Something like:
Take vial, add 5 grams of material to vial and weigh on analytic scale. Do a mega decarb in a closed vessel that has enough headspace to not pop. Weigh container after cooling and venting (in that order to ensure terpene recondensing). Weight loss would indicate incomplete. No reason to bring anything to 115 psi to check completion