Entropy is a state function, that is, its value does not depend on the past history of the system. The entropy change for an infinitesimal reversible process is given by:
where: dS = change in entropy
= heat absorbed from surroundings
in a reversible process
T = system temperature
Most processes are not truly reversible and there is a net change in entropy when going from one state to the next. Entropy can be visualized as a measure of the disorder of a system. At equilibrium, the entropy of a system is at its minimum value.
Entropies for both liquids and vapors in PRO/II are computed as functions of the enthalpies using an equation of state or generalized correlation. They are used for isentropic calculations involving compressors and expanders and for free energy minimization reactors.
Available methods for calculating vapor entropy are listed below. Refer "Entropy" under "Basic Principles" in Volume 1, Chapter 2 of the PRO/II Reference Manual for more information on entropies.
|