Work transfer in free expansion of gas - Thermodynamics

Q.  In free expansion of gas, the work transfer is
- Published on 20 Aug 15

a. negative
b. zero
c. positive
d. none of the above

ANSWER: zero
When a gas is expanded against vacuum then this expansion is called as free expansion. Work transfer is a boundary function as it is determined only at boundary. Let us consider a gas is separated from vacuum by a partition. Consider this as a system. When this partition is removed, the gas quickly fills up the vacuum area. If we do not consider the work related to removing the partition, then there is no work transfer involved here, because no work crosses the system boundary. Work is done by a system to overcome some resistance and to fill up the vacuum there is no any resistance to the gas to overcome. Therefore work transfer is zero in free expansion.

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