Little Physics Question....?

Question

When an ideal gas undergoes a slow isothermal expansion:

a) the work done by the gas is the same as the energy absorbed as heat
b) the work done by the environment is the same as the energy absorbed as heat
c) the increase in internal energy is the same as the heat absorbed
d) the increase in internal energy is the same as the work done by the gas
e) the increase in internal energy is the same as the work done by the environment

Answer 1

Kinda depends on whether it's 'free' expansion or constrained against a load such as a piston. See the ref.
In either case, there is no change in internal energy, which in an ideal gas is only a function of temperature, which by definition of isothermal, stays the same.
If free, no work is done and no heat flows into or out of the system; thus all answers are true; 0 = 0. (This is, by the way, an irreversible process; it takes work to restore the original state.)
If constrained, work is done but there is still no change in internal energy, so c, d and e are false. The answer is a. Not b because work done by the environment is negative and heat energy absorbed by the gas is positive.