GATE 2016 ME (ME2) – Question 54
A piston-cylinder device initially contains 0.4 m3 of air (to be treated as an ideal gas) at 100 kPa and 80 oC. The air is now isothermally compressed to 0.1 m3. The work done during this process is ________ kJ. (Take the sign convention such that work done on the system is negative)
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Correct answer: -55.6 to -55.4
Explanation
For a quasistatic isothermal ideal-gas process, pV=p1V1=40kJ. Work by the gas is p1V1ln(V2/V1)=40ln(0.1/0.4)=−55.4518kJ. The requested convention also makes compression work negative, so **−55.452kJ**. The standard reversible-path assumption is needed to determine boundary work from these states.