A gas expands adiabatically and does 10 J of work then the change in internal energy is:
Correct answer: B. -10J
- A. 10J
- B. -10J
- C. 20J
- D. 0J
Explanation
In an adiabatic expansion Q is zero, so from Q equal to delta U plus W, delta U equals minus W, which is minus 10 J. The gas does the work using its own internal energy, which falls, so the change is negative rather than plus 10 J.
This question appeared on the UHS MDCAT 2026 paper, which you can sit online with every answer explained.
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About First Law of Thermodynamics
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
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