A flask with a volume of 2.40 L , provided with a stopcock, contains ethane gas

Question

A flask with a volume of 2.40 L , provided with a stopcock, contains ethane gas (C2H6) at a temperature of 297 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.

Problem 15.77 Part A A flask with a volume of 2.40 L, provided with a stopcock, contains ethane gas (C2H6) at a temperature of 297 K and atmospheric pressure 1.013x105 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 What is the final pressure of the ethane in the flask? p2 Submit My Answers Give Up Part B Find the mass of ethane remaining in the flask. m= Submit My Answers Give Up de Feedba Continue

Explanation / Answer

Using ideal gas law:

PV = nRT

n = PV/RT

no of moles in cold flask is

n1 = 1.013*10^5*2.4*10^-3/(8.314*297) = 0.09846 moles

no of moles in hot flask is

n2 = 1.013*10^5*2.4*10^-3/(8.314*313) = 0.09343 moles

final pressure when hot flask is cooled, will be given by:

Pf = n2*R*T/V

Pf = 0.09343*8.314*297/(2.4*10^-3) = 96126.16 Pa = 0.96*10^5 Pa

2.

Mass of ethane will be

m = n2*M

m = 0.09343*30.1 = 2.81 gm

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