The first law of thermodynamics [itex] dU=dQ-dW[/itex] could be expanded to [itex] dU=TdS-PdV[/itex] where U is internal energy, T is temperature, S is entropy, P is pressure, and V is volume. I am trying to understand the terms one by one in plain English. So: V is how big the container is, P is how hard the container is pushing the system, U is internal energy of system, T is how willing the system want to give out heat, and S is how evenly distributed the thermal energy is. Plus: [itex]PdV[/itex] is energy (loss) due to the system pushes out the surroundings to make itself a room, and [itex]TdS[/itex] is energy due to the particles jumping around. Is there misconception? and I don't understand why [itex]TdS[/itex] would be a form of energy, why?