Is a reversible isothermal process truly without energy change?

[chukie]

Hi!
I was just wondering if in a reversible isothermal process, there is a change in internal energy.
I know that for the isothermal forward process the temperature is constant so internal energy is constant? What really stumps me is the word reversible.

 

[Mapes]

In general, yes, the internal energy can change in a reversible isothermal process. (An exception exists for the case of an ideal gas, whose internal energy is a function of temperature only.)