Free expansion process of gas within system - Thermodynamics

Q.  Free expansion of gas within a system is
- Published on 20 Aug 15

a. a reversible process
b. an irreversible process
c. a quasi-static process
d. none of the above

ANSWER: an irreversible process

Free expansion of gas

Consider the above diagram, a system contains gas in the compartment 1 and vacuum is separated by a diaphragm in compartment 2. If the diaphragm is removed then the gas in compartment 1 will expand into the compartment 2 until the pressure in both the compartments will become equal. This is a spontaneous process.

It is not possible to return the gas in the compartment 2 into the compartment 1 with increase in the pressure, without any other effect on the system. To return this process, the external work has to be done on the system. Therefore it a irreversible process.

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