ABSTRACT
Appendix ........................................................................................................... 161 Keywords .......................................................................................................... 161 References ......................................................................................................... 162
7.1 THERMODYNAMICS OF NON-EQUILIBRIUM PROCESSES
Thermodynamics of equilibrium is extended to processes taking place near to equilibrium. We recapitulate very briefly, thermodynamics of equilibrium. In a system consisting of one component, Gibbs free energy is just a function of pressure P and temperature T 1
g = g(P,T)
g = h – Ts
dg = – sdT + vdP (1)
Under isothermal-isobaric conditions, it follows:
dg = – Tds ≤ 0 (2)
The Equation (2) shows, Gibbs free energy is minimum in equilibrium. This minimum principle is a consequence of 2nd Law. More precisely, we write Equation (2) as:
dg = – Tdi s ≤ 0 (2a)
where di s represents the internally produced entropy in the system with:
di s ≥ 0
positive for irreversible processes and zero for reversible ones. For non-equilibrium situations, but situations near to equilibrium, we assume
that all thermodynamic equations are also valid. The only generalization, we have to make: There are more than two independent variables since non-equilibrium situations are characterized by additional variables. For example, a system not in equilibrium with respect to temperature does not have one (constant) temperature. It is characterized by many different temperatures (a gradient of temperature) leading to conductance of heat. In what follows, we will not discuss those inho-
1 Note extensive quantities are symbolized by letters, intensive quantities by capitals.
