Left: American engineer Willard Gibbs' 1873 graph of the of the energy ε verses the entropy η of a body showing the available energy of a body, section AB, at an entropy of D, a type of energy that would famously be labeled as "free energy" by German physicist Hermann Helmholtz in 1882. [1] Right: Irish physicist James Maxwell's 1875 addition of the volume axis, shown perpendicular to the plane here, and used sunlight and shadows, to make a three-dimensional thermodynamic surface. |
MN = the section of the surface of dissipated energy.
AD = the energy of the body in its initial state.
AE = the entropy of the body in its initial state.
AB = its available energy.
AC = its capacity for entropy.
“At the beginning, the chemical energy of the coal is free, in the sense that it is available to us for producing some mechanical work. In the process, however, the free energy loses this quality, bit by bit. Ultimately, it always dissipates completely into the whole system where it becomes bound energy, that is, energy which we can no longer use for the same purpose.”