Question

Calculate the work done when one mole of gas is allowed to expand freely in vacuum.

• A. 20 J
• B. 0 J
• C. 10 J
• D. none of the above

Answer 1

The correct option is B 0 J

Gas expands in vacuum, so it is a case of free expansion i.e., $P_{ext}=0$ and thus, it is an irreversible process.
Therefore, $W=-P_{ext}(V_2-V_1)=0$
In free expansion, the gas is expanding in vaccuum and the molecules move freely i.e the gas expands against no force.