Sciencemadness Discussion Board

formula for calculating amount of compressed gas

nikotyna1939 - 10-4-2019 at 20:46

i want to know what is the formula for calculating amount of compressed gas at 25 Celsius and 100 bar inside 10 liter gas cylinder filled with methane, hydrogen and oxygen. also i mean how much cubic of gas can be filled inside the cylinder ,the purity is 100 percent and also each cylinder is separate gas not mixed


[Edited on 11-4-2019 by nikotyna1939]

[Edited on 11-4-2019 by nikotyna1939]

Ubya - 10-4-2019 at 22:37

to answer i need the partial pressure of each gas.
what's the percentage of each gas?

Deathunter88 - 10-4-2019 at 23:24

Quote: Originally posted by Ubya  
to answer i need the partial pressure of each gas.
what's the percentage of each gas?


For a good estimate, this is not needed. Just multiply the pressure in ATM by the volume of the cylinder. In your case 100bar is about 99atm. 99atm*10L=990L of gas.

Ubya - 11-4-2019 at 01:59
Quote:

The general equation of state of an
ideal gas that is used in partial pressure mixing, Boyle's law, states that the quantity (P*V) is a constant at
constant temperature. This equation must be corrected to address the behavior of real gases under high
pressure. Thus the expression:
P1* V1 = P2* V2
needs a supplementary factor, the compressibility factor Z. If Z is less than 1 gases can be more easily
compressed than gases with Z values greater than 1. The equation of state now becomes:
(P1* V1) / Z1 = (P2* V2) / Z2
The Z value for oxygen at 165 bar (2400 psi) and 20°C is 0.941. Using the above equation, a gas cylinder
with a volume of 5.7 liters (~40 ft3
@ 3000 psig) filled with oxygen to 165 bar would contain the
equivalent of 999.5 liters of oxygen at 1 atmosphere instead of 940.5 liters calculated by the use of
Boyle's law.

It's not a good estimate multiplying the volume at a certain pressure for the new pressure, it's not that simple, otherwise PV=nRT would be already more than enough for everything.
I thought nicotyna needed a better answer than "a bunch of gas"

Tsjerk - 11-4-2019 at 08:08

Don't calculate, or has been measured.

First hit when googling "pressure density gas methane graph"

link





[Edited on 11-4-2019 by Tsjerk]

CharlieA - 11-4-2019 at 15:34

Doesn't it say in the original post that each gas is in separate cylinder? In which case I would think that PV = nRT would apply.

Ubya - 11-4-2019 at 15:48

Quote: Originally posted by CharlieA  
Doesn't it say in the original post that each gas is in separate cylinder? In which case I would think that PV = nRT would apply.


edited his post, in the beginning it sounded like it was just one cylinder with a mixture of gases

Plunkett - 12-4-2019 at 06:43

Quote: Originally posted by CharlieA  
Doesn't it say in the original post that each gas is in separate cylinder? In which case I would think that PV = nRT would apply.

The ideal gas law starts to fall apart at low temperatures/high pressures where intermolecular forces become more significant. There are equations that accommodate for intermolecular forces (which I am not in the least bit qualified to talk about), but for more common gases like methane, hydrogen and oxygen it is often easier to look up a chart like the one Tsjerk linked to.

[Edited on 12-4-2019 by Plunkett]