question_answer

A gas does work during isothermal expansion. What is the source of mechanical energy so produced?

Answer:

                By first law of thermodynamics, \[\Delta Q=\Delta U+\Delta W.\]But for an isothermal process, \[\Delta U=0,\]so\[\Delta W=\Delta Q\]. Thus the energy required for doing mechanical work during an isothermal process is obtained as heat by the gas from the surroundings.