The internal energy of an ideal gas decreases by the same amount as the work done by the system.

1. The internal energy of an ideal gas is proportional to the temperature. Since internal energy is decreasing, therefore, the temperature must decrease.


2. According to the question, change in internal energy is equal to change in work done.


3. According to First law of thermodynamics,


ΔQ=ΔU+ΔW


Where ΔQ=heat supplied/extracted to/from the system


ΔU=change in internal energy


ΔW=work done by/on the system


4. We know for adiabatic process ΔQ=0. So, from first law ΔU=ΔW.

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