Dear Oscar,<br><br>If we look at the very definitions of work and heat, it is the "pulley work" which defines thermodynamic work. So, as an example, if we take an empty box, fill it with gas at a pressure greater than surrounding's and isolate it (which means no heat or work should escape from or into the box), box becomes an isolated system. Now, puncture the box (or make a small hole/outlet which has smooth curvature so that heat does not generate when the gas escapes from the box), and allow the gas to escape until steady state is reached. Obviously, final pressure between the box(system) and the surroundings(atmosphere) will be the same. But the escaped gas cannot enter the box and bring the pressure to its initial value "automatically" without external work. As entropy can be defined as unavilability of work that has been done, "free expansion" discussed above may be considered as a process where no heat or work is done but entropy is still generated. <br><br>I hope I answered your question and I welcome any comments or flaws in my reasoning or understanding of this tricky concept of entropy from anyone!<br><br>BYE