Nonequilibrium nanothermodynamics

Entropy production for a system outside the thermodynamic limit is formulated using Hill's nanothermodynamics, in which a macroscopic ensemble of such systems is considered. The external influence of the environment on the average nanosystem is connected to irreversible work with an explicit formula based on the Jarzynski equality. The entropy production retains its usual form as a sum of products of fluxes and forces and Onsager's symmetry principle is proven to hold for the average nanosystem, if it is assumed to be valid for the macroscopic ensemble, by two methods. The first one provides expressions that relate the coefficients of the two systems. The second gives a general condition for a system under an external force to preserve Onsager's symmetry.