Fluxes of Thermodynamic Parameters

In general cases, the local rate (per unit volume) of entropy production through internal transformations in the system is determined from the equation 

IfP = Ta is the local rate of energy dissipation (per unit volume), then, obviously. 

Sometimes thermodynamic forces are related direcdy to a Xj = When this is the case, X, = TX,. 

In aU cases, the rate of entropy production per isothermal unit volume at temperature T is described by the relationship 

The thermodynamic force (affinity) X is a pivotal concept in thermo dynamics of nonequilibrium processes because of its relationship to the concept of driving force of a particular irreversible process. Evidently, thermodynamic forces arise in spatially inhomogeneous systems with, for example, temperature, concentration, or pressure inhomogeneity. In spatially uniform homogeneous systems, such forces arise either in the presence of chemically reactive components that have not reached thermodynamic equiHbrium via respective chemical transformations or at the thermodynamic possibility of some phase transformations. 

---

It was just shown that fluxes of thermodynamic parameters that describe transformations in chemically reactive systems are in direct relationships with the rate of chemical reactions. The relationship between the rate of a chemical reaction and physicochemical parameters (reactant concentra tions, temperature, etc.) of the system is the subject of a special branch of physical chemistry called chemical kinetics. 

---