Gas laws physics question - help
Question:
A cylinder of gas has a mass of 10kg and a pressure of 8 atmospheres at 27 degrees (Celsius). When some gas is used in a cold room at -3 degrees (Celsius), the gas remaining in the cylinder at this temperature has a pressure of 6.4 atmospheres. Calculate the mass of gas used.
My somewhat of an attempt:
initial no. of moles: n=PV/RT=Pm/RTx , were x is the density of the gas and m, the mass, R, ideal gas constant.
Final no. of moles: n=P'm'/RT'x
equating and solving for m'. m' = T'Pm/P'T
so I sub in the values and get m' as 11.25kg which makes no sense.
Please explain what I'm doing wrong.
Thanks in advance
A cylinder of gas has a mass of 10kg and a pressure of 8 atmospheres at 27 degrees (Celsius). When some gas is used in a cold room at -3 degrees (Celsius), the gas remaining in the cylinder at this temperature has a pressure of 6.4 atmospheres. Calculate the mass of gas used.
My somewhat of an attempt:
initial no. of moles: n=PV/RT=Pm/RTx , were x is the density of the gas and m, the mass, R, ideal gas constant.
Final no. of moles: n=P'm'/RT'x
equating and solving for m'. m' = T'Pm/P'T
so I sub in the values and get m' as 11.25kg which makes no sense.
Please explain what I'm doing wrong.
Thanks in advance
Original post by arson_fire
Your assuming the number of moles is constant, but you lose some gas so its not. Hint - does the volume of the cylinder change?
Thanks, so i did this.
Assuming V is constant
V= nRT/P=mRT/P(Mr)
Mr is the molecular mass of the gas.
Initial volume = final
(10kg)RT/P(Mr) = (10-m)RT'/P'(Mr)
Simplifying for m
m=10-(10TP'/PT')
Got 1.1kg which is the correct answer, thanks.
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