increases. Conversely, if the system expands (i.e., system surrounding expansion, so free expansions not the case), then the work is negative as the system does work on the surroundings.

It is also worth noting that for ideal gases, if the temperature is held constant, the internal energy of the system U also is constant, and so ?U = 0. Since the first law of thermodynamics states that ?U = Q + W in IUPAC