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Inorganic : gases
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 Message 1 of 3 in Discussion 
From: dianna  (Original Message)Sent: 12/18/2004 6:30 AM
i'm not sure if i'm doing this question right
Gas cylinder A has a volume of 48.2L and contains N2(g) at 8.35atm at 25 degrees. Gas cylinder B of unknown volume contains He(g) at 9.5atm at 25degrees. When the two cylinders are connected and the gases mixed, the pressure in each cylinder becomes 8.71atm. What is the volume of cylinder B?
 
can i find Vtotal and then subtract the volume of A away from the total to find volume of B, by setting the question up like this:
48.2L/Vtotal= 8.35atm(pressure of A)/17.85atm(pressure of A+B)
 
thanx a bunch


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Sent: 12/18/2004 8:51 AM
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 Message 3 of 3 in Discussion 
From: MSN Nickname·Steve·Sent: 12/18/2004 9:31 AM
Ack!  I used the wrong temperature the first time, so here it is again using T = 298.15 K ! 
 
 
Something like that can work, but it may be easier to just use PV = nRT before and after mixing:

1.  Before allowing the gases to mix,

     moles of gas A,  nA  =  PAVA / RT  =  16.4500 moles

     moles of gas B,  nB  =  PBVB / RT  =  0.388291 VB moles


2.  After allowing the gases to mix,

     PTVT  =  nTRT

     where PT  =  8.71 atm,  VT  =  48.2 L  +  VB,  and  nT  =  16.4500 moles  +  0.388291 VB moles.
 
     Or, plugging in the numbers and leaving off the units for simplicity, we'll have

     (8.71) (48.2 + VB)  =  (16.4500 + 0.388291 VB) (0.08206) (298.15)

     From which we can get VB.
 
 
Steve