So energy will disperse because all these molecules carry energy. In this case, all the molecules were localized in the bag. So all the energy that the molecules carry was localized in the bag. But now the molecules are dispersed, and so the energy is also dispersed throughout this larger region of space. Now, the protein molecules, even though they want to leave that bag, cannot leave that bag because of that physical barrier. They are simply too large to pass across those tiny pores in that semipermeable membrane.