I used to imagine enthalpy & entropy as the (un)usable energy of gas molecules that vibrate. But now I feel the real picture is more spiritual than that. I got that feeling while learning hydrolysis of ATP. It just releases usable energy, (just like that) to macromolecules which are too huge to be vibrating like we think about gas molecules. It doesn’t seem like vibrations are getting transferred. WTF is energy?