Hi Everyone, quick intro. I am taking thermodynamics (chemical engineering style, college) and am just generally confused by the concepts such as T, U, H, S, fugacity, etc, so I decided to revise my understanding and work my way up from classical physics. and I need some help with that. I will update this post every time a concept is made clear. The way I propose to understand these concepts are simple thought experiments, and then put these concepts in different examples. 1. Temperature (?) What is temperature? Building on my previous knowledge from high school physics and college physics, the temperature of a molecule is proportional to the translational kinetic energy of the molecule. This does not rotational energy. But does this include vibrational energy? What type of energy does this include if at absolute zero there is supposed to be zero energy (besides quantum)? 2. Energy (?) Assuming a single molecule flying around in some fixed volume V, how many different forms of energy are present? Assuming no change to the mass, or actual molecule? Mass energy - mc^2 , Do not consider (DNC) Bond energy - energy stored in bonds, defined by bond-enthalpy, (DNC) (includes torsional forces) *I have read in a Material Science Engineering journal that increasing temperature stresses the bonds in molecules. What is the mechanism for this? It was for color changing materials.* Vibrations of the molecule - defining vibrations as movement from one axis to the opposite axis from the center of the molecule (not intermolecular stretching). Rotation of the molecule - rotating about the center of mass of the molecule. This is important for atoms, but I am not sure about molecules. Translational motion - analgous to drift velocity of an electron. Assuming constant velocity, the velocity away from the center of the molecule. These are all the energies I can think of. Now, of these energies, which contribute to temperature, and which contribute to internal energy? (I am aware of that for an ideal gas, internal energy is a function of temperature, but I am just trying to be as general as possible) Pressure, enthalpy, and entropy will be followed up as soon I understand the above concepts. Thank you for all your help!