In an isothermal expansion of an ideal gas
Correct answer: C. the temperature and therefore the internal energy stay constant, so the heat supplied equals the work done
- A. the internal energy falls
- B. no heat is exchanged
- C. the temperature and therefore the internal energy stay constant, so the heat supplied equals the work done
- D. the work done is zero
Explanation
Constant temperature means constant internal energy for an ideal gas, so by the first law every joule of heat entering leaves again as work done pushing back the surroundings. The process must be slow and the container a good conductor for the temperature to be held fixed. A process with no heat exchange at all is adiabatic, not isothermal.
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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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