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What pressure is exerted by 8g (eight grams) of $N_2O$ gas on the walls of a container that has about 0.5l (half of liter) of volume? Will the pressure be the same in case of 8g of $CO_2$ gas?

Background: I have a Hendi whipped cream maker that uses 8g $N_2O$ charges to make whipped cream. I am thinking about trying to use it to make soda water (with 8g $CO_2$ charges). The manual does not say anything about $CO_2$ charges, so I am wondering if it's safe as far as the pressures go. Also note that the container itself is a little larger than 0.5l but I was not sure as for the exact volume, so I settled down on 0.5l here.

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The $CO_2$ and $N_2O$ have about the same amount of mols per gram. 0.1817789 mol for 8 grams of $CO_2$ and 0,1817653 mol for 8 grams of $N2O$.

at ~$22^oC$ this gives an approximate pressure of 8.9 bar according to the ideal gas-law $ P = \frac{nRT}{V}$.

However whipped cream and water are quite different, whipped cream in equal volumes is more easily compressed than water could be. What I would be worried about is that if you fill the container mostly with water that the effective volume is going to be much less than 0.5l causing a much greater pressure than 9 bar. To be honest this things tend to be safe up to much greater pressures though, especially if you have a higher quality one, they also often release overpressure through the front nozzle. Still be very careful with what you do.

Usually they have a high safety factor for many reasons, misuse being one of them XD

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    $\begingroup$ "The user did not take into account that the water does not compress easily" is what I would expect to read in a post-mortem report, therefore I won't be trying to make the soda. Thanks for pointing this out! $\endgroup$
    – lukeg
    May 30, 2018 at 17:03
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    $\begingroup$ Liquid cream and water dont compress all that differently, maybe a tiny bit. (I think) Bob’s big concern was a volume of puffed-up, already-whipped cream being compared in volume to water . If you can compare the weight of liquid water to the weight of cream in the can, it should limit that aspect of uncertainty. Or settled liquids. Dunno if you can easily. The real issue is density differences if you compare weights. Cream is 3% more dense so equal weight takes up more space. Reduce your water weight by five percent if working with weight. Skip it if not $\endgroup$
    – Al Brown
    Jul 30, 2021 at 21:30
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These devices should only be used for their intended purpose. If you wish to carbonate water you ought to use a soda (or "seltzer") siphon instead, or another suitable device. There are differences in design specifically chosen for each application. For example, a whipcreamer is held upside down when dispensing the foam and has a small piston in the head that opens up to let the cream through. A soda siphon is held upright and has the water forced through a tube that descends from the head into the bottle down to the bottom. If you attempt to switch their functions then in the best case you get a suboptimal result or a messy process, in a slightly worse case you may damage the device and in the worst case you could risk injury or even death.

Unfortunately that last bit is not an exaggeration seeing how a 33-year old woman died in 2017 after an accident with a whipped cream dispenser. Aside from that incident there are reports of serious injuries sustained after a mishap with one of these tools. Some of it may have been due to improper use or failure to follow the instructions, some of it was possibly a malfunction. At any rate it serves as a warning to take no risks with something that operates through pressurized gas.

As for Bob van de Voort's answer, the two gases may indeed have a very similar pressure so that in itself may not pose a problem. Neither would the difference in compressibility of the liquids. These dispensers work by filling them up with liquid cream, which wouldn't differ much from water in how easily (or rather not) it is compressed. The liquid can go up to a maximum amount indicated on the bottle. There is then plenty of headroom left for the gas. The head is screwed on and only then is the N2O gas injected and mixed with the cream. So you make the whipped cream in the dispenser (and likely to some extent while it is being pushed out the siphon) rather than filling it initially with whipped cream. The final difference in internal pressure between water with CO2 and cream with N2O shouldn't be much given that the initial amount of liquid is the same, both types of cartridges contain 8 grams of gas and both have almost the same mols per gram.

But for the sake of safety you should make no assumptions and shouldn't have to rely on such considerations. There can still be other differences you might not have taken into account, such as the materials used, the construction and how these respond to the different gases. A mistake is easily made if you stray from the instructions. For example, when I purchased a whipped cream dispenser I believed it would also make for delicious creamy cold brew nitro coffee, rather than buying a much more expensive, hip specialized device. While I can certainly put coffee in it with N2O, I failed to realize that drinks like nitro coffee or Guinness use nitrogen, a different gas. And one that does have a very different molar mass. Trying to use nitro anyway would either be very ineffective (assuming the cartridge would even fit) or effective to the point that I might never require another coffee again.

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