2 replies to this topic

[jonol92]

The question as written:

"A fully sealed 50m^3 room at atmospheric pressure and temperature 20C contains two ballons, one containing helium and the other containing oxygen. The balloons each have a volume of 0.5m^3 and have gauge pressure 2m of water. The balloons are ruptured and helium and oxygen mix with the air in the room.

Determine mass and mol fractions of the gaseous species in the room, assuming that air contains 79% nitrogen and 21% oxygen by volume and atmospheric pressure is 100kPa.

Universal gas constant = 8.314
Atomic molar mass He = 4 g/mol"

I can determine a number of things using ideal gas laws from this but dont seem to be getting the answers required. Can anyone give me a step by step on how to see this questions through (im not asking for you to do tha calculations, just for guidance on the path to take)? THANKS

[Shivshankar]

Jonal92,

Can you put your calculation sheet here so we can correct you? The best practice is to put your calaculation work copy.

At the moment please have a look on following link, which will solve your query.

http://www.cambridge...d/chapter 9.pdf

Regards
Shivshankar

[kkala]

Some hints, probably useful to start.
1. Total air volume 50-2*0.5=49 m3, pressure=1 bar a, temperature=20 oC=293.15 oK
2. Ideal gas molar volume = 22.414*(1.01325/1.00)*(293.15/273.15)=24.374 m3/kgmol under said conditions.
3. kgmols of air: 49/24.374=2.010 (79% N2 and 21% O2).
4. Gas pressure in balloons 2/10 kgf/cm2 g =1+0.2*0.980665 bar a= 1.1961 bara, temperature=20 oC, volume of each balloon =0.5 m3. Molar volume can be found as above for these conditions, then kgmols of He and O2.
5. So you can calculate kgmols of N2, O2, He in the resulting mixture, then proceed.

Note: Alternatively you can calculate kgmols n from ideal gas low PV=nRT, instead of using molar volume. For instance, concerning air
n=49*1E5/(8314*293.15) (m3*Pa/J)*kgmol =2.010 kgmol
where R=8.314 kJ/kgmol/oK=8314 J/kgmol/oK.