ABSTRACT
Until now we considered equilibrium states and reversible processes that are sequences of equilibrium states. This is, however, not what happens in real processes. This chapter shows how to include irreversibility in the framework of linear nonequilibrium thermodynamics. Nonequilibrium states of an isolated system are (macroscopic) states whose probability distribution, {wi}, deviates from the equilibrium distribution, {w(eq)i }. State changes, which go through nonequilibrium states are nonequilibrium processes. An example is relaxation to equilibrium. In practice, nonequilibrium processes often occur as an interplay of forces which drive the state away from equilibrium, and a response of the system which tries to restore equilibrium. This response looks like a counter-force which pulls the state towards the entropy maximum. We will look at two scenarios that are very important, namely, at steady state currents, and also briefly at exponential relaxation.
