This may be a matter of me being confused by the definition of heat. However, I view heat as the energy passed between systems of different temperatures. My problem is the following: By the principle of minimum energy/max entropy, in an isolated system (and therefore fixed internal energy). the entropy of the system should tend to maximize. I thought of a very simple example. I have a bunch of charged positive particles all initially pretty close together. As time goes on they will separate, and their potential energies will drop. However, they will all have gained kinetic ( thermal) energy and hence the temperature will have increased and the entropy of the system will have also clearly increased. (Fast movement and particles now clearly in a state of higher disorder). However, change in entropy is defined as q/T. However, where could this heat q have come from? I understand the obvious that the potential energy of the charged particles was converted into kinetic, but this comes from the work done on the particles does it not? There is no outside system to transfer heat?