Question

A gas does work during isothermal expansion. The source of mechanical energy so produced is the internal energy of the gas itself.

(a) True

(b) False

This question was addressed to me during an interview.

My question is from Thermal Equilibrium in section Kinetic Theory of Gases of Engineering Physics I

Answer 1

The correct choice is (b) False

For explanation I would say: By the first law of thermodynamics,

∆Q=∆U+∆W.

But for an isothermal process, ∆U is zero, so ∆Q=∆W. Thus the energy required for doing mechanical work during an isothermal process is obtained as heat by the gas from the surroundings.