15.81 A flask with a volume of 2.20 L , provided with a stopcock, contains ethan

Question

15.81

A flask with a volume of 2.20 L , provided with a stopcock, contains ethane gas (C2H6) at a temperature of 300 K and atmospheric pressure 1.013×105 Pa . The molar mass of ethane is 30.1 g/mol . The system is warmed to a temperature of 393 K , with the stopcock open to the atmosphere. The stopcock is then closed, and the flask cooled to its original temperature.

Part A

What is the final pressure of the ethane in the flask?

answer: P2= ______ Pa

Part B

Find the mass of ethane remaining in the flask.

answer: m=______ g

Explanation / Answer

moles in flask at 300 K= = PV/RT = 1*2.20/(0.0821*300) = 0.0893 mol
moles in flask at 393 K = PV/RT = 1*2.2/(0.0821*393) =.0681 mol
final pressure = nRT/V = .0681*0.0821*300/2.2 = 0.762 atm = 7.62*10^4 Pa
mass or ethane = moles*MM = .0681*30.1 = 2.04 g

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