Solve using the method in the hint Hint: Use the first law of thermodynamics equ

Question

Solve using the method in the hint

Hint: Use the first law of thermodynamics equation and entropy. Assume the entropy of the remaining gas doesn't change. Find the entropy change on cooling and this will give you an equation. Also, use the entropy change on liquefying and this also will give you another equation. Combine the two equations with the help of other simple equations and you will find the initial pressure. This problem can be solved with five equations.

A flask contains helium gas at 11 K. The flask is thermally isolated and the gas is allowed to escape slowly through a narrow tube until the pressure within the flask is 0.98 atm and the temperature is 4.2K. If the gas is ideal, find the initial pressure for the flask to be entirely filled with liquid at the end of the process.

Explanation / Answer

from

gas law..

P1V1/T1 = P2V2/T2

V is constant

so P1 = P2T1/T2

P1= 0.98*11/4.2

P1 = 2.56 atm

P1 = 2.56 atm

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