Equilibrium thermodynamics for porous media is considered with special
emphasis on its basis in pore-scale thermodynamics. It is shown that
porosity, the new purely macroscopic variable, enters the relations on
the same footing as mass densities and the strain tensors. Biot's use
of elastic energy potential, which lies at the foundation of his theo
ry of poroelasticity, is examined in light of the results obtained her
e.