Sciencemadness Discussion Board

Compression of gases (H2) by ATMs - how it works

RogueRose - 4-4-2017 at 17:07

I'm trying to figure out how much gas there is in a cylinder of H2 or O2 or any gas (but mainly H2 now..)

At 1 ATM of pressure and 70 deg F 1lb of H2 occupies 192 ft^3

Does doubling the pressure allow doubling the cubic feet of gas in the same space?

Or does each ATM allow for an additional ft^3 of gas to occupy the same space?

In the example I gave with the 192 ft^3 - would that be 192 ATM for the gas to occupy 1ft ^3?

Corrosive Joeseph - 4-4-2017 at 17:16

https://en.wikipedia.org/wiki/Gas_laws


/CJ

PirateDocBrown - 5-4-2017 at 06:17

Gods, please learn to work in the Metric System.

PV=nRT, the Ideal Gas Law, can be used to approximate real gasses.

If P (pressure) = 101.325 kPa = 1 atm, and
n = 1 mole, and
T = 273.15 K = 0 C, then

R, the Ideal Gas Constant, would dictate a V, (volume) of 22.4 liters.

If your freshman chem prof didn't teach you this, you need to take it again.

Plug in whatever numbers you have, and you can balance the equation for any conditions.


[Edited on 4/5/17 by PirateDocBrown]

[Edited on 4/5/17 by PirateDocBrown]

Praxichys - 5-4-2017 at 08:35

Boyle's law:

P1V1=P2V2

10 liters at 1atm = 1 liter at 10atm

Both contain the same mass of gas.

Keep in mind that these equations only apply to "ideal" gases. Most gases behave approximately ideally until you get to the extremes of temperature and pressure.

RogueRose - 6-4-2017 at 21:55

Quote: Originally posted by Praxichys  
Boyle's law:

P1V1=P2V2

10 liters at 1atm = 1 liter at 10atm

Both contain the same mass of gas.

Keep in mind that these equations only apply to "ideal" gases. Most gases behave approximately ideally until you get to the extremes of temperature and pressure.


Thank you Prax! That is exactly what I was wondering.

Just so some people know, some people have a VERY difficult time understanding equations when variables are used, especially when there are repeats of the same symbol (using n - number) and especially when they don't fully understand the topic. It is somewhat like dyslexia or reading a foreign language w/ dyslexia. This is more common than many would think for people who don't deal with sciences or "higher" level math on a daily basis.

Thanks again for they explanation, I appreciate it.

tsathoggua1 - 7-4-2017 at 11:41

Regarding the comparison w/ dyslexia, the mathematical equivalent is called dyscalculia. Or acalculia when ability to process mathematical operations is completely ablated. I have it, to the degree its just about still dyscalculia. Always have had severe dyscalculia. After some very unpleasant 'happenings' several years (as good as I can get, my sense of time went with what numerical ability I did have, likewise hunger although the last isn't quite so badly fucked, I can just go for days without eating and not realize it, and not feel hungry, and so, until somebody comments I haven't eaten in a week or so, not be aware since I've very little reminder of the fact. Even then, often enough just the thought of food is enough to put me off, like not wanting any more food when somebody is stuffed. Memory is screwed up as well, and when things are presented in algebraic form, I usually won't be able to 'see' it.

For example I can 'feel' the explanation given as its worded above of Boyle's law, but were I can't correlate it to the same thing when presented in numerical or algebraic format. Its kind of like, from a cognitive processing point of view, blindness, in that I can feel something out and work out its shape, but otherwise unable to perceive anything other than the actual written characters. But otherwise I might as well be trying to peer through a sheet of lead in the visible wavelength range.

For a chemist, its no end of bloody frustrating. Thankfully I'm not completely acalculic, but not all that far off. Most math I have to memorize by rote for practical purposes, or have someone else tell me how the calculation is done, write it down and use a calculator. Its a gigantic pain in the arse. And things like taking down phone numbers are a nightmare if I have to read them myself, as the numbers 'move' in both the minds eye and the physical ones. The one that more or less works anyway.

JJay - 8-4-2017 at 07:04

As I see it, chemistry mostly is just math. If you take the math out of it, it's like looking at rocks or something....

I memorized this formulation of the ideal gas law a long time ago:

P1*V1/(n1*T1)=P2*V2/(n2*T2)

P = pressure
V = volume
n = number of moles of gas
T = temperature (degrees Kelvin above absolute 0)

This is usually formulated as PV=nRT with only one gas where R is something called the Ideal Gas Constant, but if you happen to have memorized how gas behaves at a particular temperature and pressure, you don't have to remember R. 1 mole of gas consumes 22.4 liters at standard temperature and pressure, 25 C (about 298 Kelvin) and 1 atmosphere (760 torr).


RogueRose - 8-4-2017 at 15:52

Quote: Originally posted by tsathoggua1  
Regarding the comparison w/ dyslexia, the mathematical equivalent is called dyscalculia. Or acalculia when ability to process mathematical operations is completely ablated. I have it, to the degree its just about still dyscalculia. Always have had severe dyscalculia. After some very unpleasant 'happenings' several years (as good as I can get, my sense of time went with what numerical ability I did have, likewise hunger although the last isn't quite so badly fucked, I can just go for days without eating and not realize it, and not feel hungry, and so, until somebody comments I haven't eaten in a week or so, not be aware since I've very little reminder of the fact. Even then, often enough just the thought of food is enough to put me off, like not wanting any more food when somebody is stuffed. Memory is screwed up as well, and when things are presented in algebraic form, I usually won't be able to 'see' it.

For example I can 'feel' the explanation given as its worded above of Boyle's law, but were I can't correlate it to the same thing when presented in numerical or algebraic format. Its kind of like, from a cognitive processing point of view, blindness, in that I can feel something out and work out its shape, but otherwise unable to perceive anything other than the actual written characters. But otherwise I might as well be trying to peer through a sheet of lead in the visible wavelength range.

For a chemist, its no end of bloody frustrating. Thankfully I'm not completely acalculic, but not all that far off. Most math I have to memorize by rote for practical purposes, or have someone else tell me how the calculation is done, write it down and use a calculator. Its a gigantic pain in the arse. And things like taking down phone numbers are a nightmare if I have to read them myself, as the numbers 'move' in both the minds eye and the physical ones. The one that more or less works anyway.


THANK YOU Tsathoggua1!!
Wow, now I know that this has a name and I'm not the only one who deals with it. I know in school there were others who had the same difficulty when looking at these equations and we were told "we just didn't know it" or "understand it" but most of us could figure out the calculations faster than those w/o the problem because we had learned how to process it with our own methods within our minds/

For me, it is kind of like an English speaking person looking at Cyrillic or maybe even Greek (although I understand Greek better). It's like having a program that can process equations when written out word for word (or binary/machine) but when converted to variables, the program doesn't translate to what it should so it looks like a lot of recognizable variables but those variables have to corresponding meaning - if that makes sense to anyone. For those who don't experience this, it is difficult to explain and even more difficult impress upon others how difficult and debilitating it is while trying to work in these fields.

This happens for chemistry and electrical formulas. As "tsathoggua1" has said, he can often almost picture the equation and work that way, which is what I do but if that same was written in a variable based formula where the same variable is used many times with say (X1^(n1-1/n2)/X2)/(X2(n^(n3*n4))/X3) - That is a made-up formula but it shows something like what some equations deal with. Even with an equation 1/4 as long/complex as this, it would be daunting.

I can do algebra in my head, even advanced algebra and some more complex math but that is after I learn the process and "write my own language" of how to deal with it in my head and how to process it.

I would not be surprised if there are almost as many, if not more, people who suffer from this than from dyslexia and may be the cause for many failures in our math and science classes in our school.