Irreversibility in the hard-spheres gas: H theorem and the Gibbs relation

An H-functional is suggested in terms of the single-particle distribution function governed by the Enskog kinetic equation. It is shown to be restricted to situations near the local equilibrium state. A generalized H-theorem valid for all initial situations is established from the point of view of a master equation for the hard-spheres gas. The thermodynamics of irreversible processes is then discussed in relation to the basic foundations of the kinetic theory of dense gases.