[Dusty23]

Hi,

I need some help please... It's been a while since i've done chemistry.

could anyone help me figure out the below example:

- gas concentration (mg/m3) in vessel after pressure change:

e.g.

Temp1= 25 degrees celcius
Temp2= 25 degrees celcius

Volume1= 5L
Volume2= 5L

Pressure1= 900mmHG
Pressure2= 760mmHG

Contaminant1= 30mg/m3
Cantaminant2= mg/m3

any info/help would be appreciated.

cheers,

Dusty

[Pelle]

Think about the general gas law. pV=nRT

The volume doesn't change, the temperatur doesn't change. R is constant. You know the pressure changes. If p goes down, what will happen to n ?

Please tell us how you solved the problem when you're done. Good luck!

[Borek]

p₁V₁=p₂V₂

Volume changes, mass of contaminant is constant.

[tonyliruhan]

though the general gas law,pv=nRT    
we know  n=pv/RT, n can be worked out
p/n=RT/v     see, the right side is constant
n is proportial to the mass of gas
then again Cantaminant=m/v
Cantaminant1/Cantaminant2=m1/m2=n1/n2

[tonyliruhan]

and n1/n2=p1/p2

[Pelle]

Borek: I was thinking contaminant escaped with over-pressure (i.e. rest of the gases), you don't think so?

[xiankai]

how could any gas escape? the vessel is supposed to a closed system.

[fishyuyue]

PV=nRT
P=(n/v)R and C=n/V
P=CRT  and  RT is a constant
P is proportional to C
P1/P2=C1/C2

[Pelle]

how could any gas escape? the vessel is supposed to a closed system.

I was thinking a vessel with valve where you released pressure by letting gas out. But I guess that would complicate things a bit.

If it was entirely closed I don't see how pressure can decrease, but not volume or temperature.

[xiankai]

there are other ways to release pressure too, like changing the altitude of the vessel.

i think this is a theoretical question, hence we do not need to factor in too many things.