[orgo814]

According to my textbook, the change in internal energy for all isothermal processes in a perfect gas is equal to zero. However, in a problem I did, for a reversible isothermal condensation (from H2O(g) to H2O(l)), I was given the change in enthalpy (delta H) and therefore according to the formula delta H = delta U + deltaNRT, there would be a change in internal energy (since we have the enthalpy and there's a change in moles of gas). Isn't this contradictory? Any help explaining this to me would be appreciated

[curiouscat]

How is a condensation an ideal gas process?

[Enthalpy]

Is it the same person who makes this confusion for the second time here?

[orgo814]

They are different questions.