Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: rc7995 on 11/02/2016 20:10:04
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Hello,
Recently started studying and wanted to check my working.
Q:At the surface, the air temperature is 15 °C and the pressure is 1000 hPa. The balloon, which has a very thin, flexible skin, is filled with 1.0 m3 of helium gas. Use the ideal gas equation of state to find how many moles of helium have been pumped into the balloon, explaining any assumption that you make.
A: P V = n R T
Rearrange to get n:
n = p V / R T
Substitute in values:
n = 1000hPa x 1m3 / 8.314 J K-1 mol-1 x 288.15K
n = 0.42 moles
0.42 moles occupy the balloon
Hopefully this is correct, otherwise I'm in trouble.
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Almost correct. You need to use R with different units.
check out this webpage which tabulates the values of R for many given units: http://www.katmarsoftware.com/gconvals.htm
recall that when you multiply out all of the values on the right hand side, the accompanying units must multiply out to moles (in this case)
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I really appreciate the reply, but could I ask you to expand?
I'm really struggling with this course [:-\]
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1000 hPa * 1 m3 * 288.18 °K * R = n moles
R must have units of moles*m–3*°K–1 (I think this is 0.0831moles*m–3*°K–1)