A Proof that essergy is the only consistent measure of potential work (for chemical systems)

 

                                    By Robert B. Evens

                                    Dartmouth College

                                                1969

 

 

Essergy is defined as

 

                       

 

Connections among essergy, availability, exergy, and free energy

 

Name

Function

Comments

Essergy

This function was formulated for the special case of an existing medium in 1878 (by Gibbs) and in general in 1962 (Ref. 12).

Availability

Formulated by Keenan in 1941, this function is shown on page 32 to be a special case of the essergy function

Exergy

Introduced by Darrieus (1930) and Keenan (1932), this function (which Keena has called the ¡°availability in steady flow¡±) was given the name ¡°exergy¡± by Rant in 1956. As shown on page 39, this function is a special case of essergy.

Free Energy

Helmholtz: E-TS

Gibbs:E+PV-TS

The functions E-TS and E+PV-TS were introduced by von Helmholtz and Gibbs (1873). These two functions are Legendre transformations of energy which were shown by Gibbs to yield useful alternate criteria of equilibrium. As measures of the potential work of systems, these two functions are shown on page 44 to represent special cases of essergy function.

 

Comments: I shall learn more about what ¡°environment¡± means exactly.