Question

An insulated container contains a gas with some initial conditions. A lid is opened which allows the gas to pass into another insulated container which was initially empty. The mass of the gas remains constant. A process is described as reversible if there is no change in entropy. Explain in detail if this process is reversible or not.

Answer 1

Solution: Since , the container are insulated, no heat transfer occurs between the gas and the external environment , and since the gas expands freely into container , there is no resistance "pushing " against it, which means no work is done on the gas as it expands . As a result , the internal energy of the Gas remains same, before and after the expansion. To return the gas to its original state , it would have to be compressed back into container. This unavoidly takes place against a resistive pressure force which means that work is required to do so. This would add energy to the gas , thereby increasing its internal energy, resulting in a temperature and pressure of the gas greater than its initial temperature and pressure. It would then have to be cooled to bring it back . This would add heat to the environment which would increase entrophy. Hence , gas can not be returned to its initial state under the reverse condition , and the process described in the problem is therefore not reversible.