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Offline zeshkani

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quick questions
« on: August 29, 2007, 11:56:31 PM »
i just have a quick question about this problem iam sure its easy, but either the teacher didnt give enough info , or iam totally lost ???

a gas mixture consists of 320mg of CH4, 175mg Ar, and 225mg Ne, the partial pressure of Ne at 300K is 8.87kPa
and iam supposed to find the volume and the total pressure of the mixture

so i solve for all the mole fractions

Ar = .123457
Ne= .314275
CH4= .562267

so the get the total pressure  i can get for Ne by this (.08754atm(8.87kPa) = .314275P) which is (P=.278546) but this is only the pressure of neon, so how can i get Ar and CH4 ? is it possible to take the ratio of (Ar + CH4 /Ne) * the total pressure of neon, which would give me total pressure of mixture, and to get volume ill just use PV=nRT

Offline Borek

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Re: quick questions
« Reply #1 on: August 30, 2007, 02:41:27 AM »
You are on the right track. Write definition of partial pressure and solve for total pressure.
« Last Edit: August 30, 2007, 03:37:09 AM by Borek »
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Offline zeshkani

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Re: quick questions
« Reply #2 on: August 31, 2007, 12:13:16 AM »
ok here is what i got when i solved it,

Offline macman104

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Re: quick questions
« Reply #3 on: September 06, 2007, 04:49:38 AM »
When you calculate your P1 = x1*P, you are not solving for PNe, you are solving for P, so when you get the answer 0.2785, that is your total pressure not the partial pressure of Ne, remember they gave that to you (8.87kPa or 0.08754 atm).

So, you already have the partial pressure of Ne.  You know the formula, P1 = x1*P, solve that for P.  Don't go to all the trouble of calculating the ratio of Ar+CH4 to Ne and such.  Also, you already know the ratio (you calculated the mole fractions).  For future reference, you just need the mole fraction of one gas and it's partial pressure to find the total pressure.  After that your golden.

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