Time needed for balloon to deflate?

Started by bmathew, December 06, 2009, 08:13:29 PM

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bmathew

It takes 14 hours for a neon filled balloon to shrink to half its original volume at 250 K and 1 atm. How long would it take to shrink to half its original volume at 1000K and 1 atm?

I thought this was a rate of effusion problem, and to compare rates of effusion you only use molar masses, so I thought it would be 14 hours, but the CORRECT answer is 7 hours. I can't find any other formulas in my notes that involve time or rates. How do you do this question?

uma

Hi Brian
Please place your new questions as different topic .this will help me .

uma

You are right this question is based on effusion only but approach is different .
here rate of effusion are compared with temp and volume
we know that
u( rms) =( 3RT/M)^1/2
now here M is same for the cases (He gas)
R is also same
(first case at T= 250K)
if u1(rms) = change in volume (half of orginal volume)/ t1(14 hours)
(second case at T= 1000K)
u2(rms) = change in volume (half of orginal volume)/ t2
now let us take ratio of both
u1/u2 =  t2/t1 =( 250/1000)^1/2 = 1/2
t2/14 hours = 1/2
t2 = 1/2 X 14 = 7 hours

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