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Reference Environment

Szargut's Reference Environment

For the calculation of the chemical exergy of any substance, a reference environment should be defined.

The Reference Environment can be assimilated to a thermodynamically dead planet where all materials have reacted, dispersed and mixed. The most common R.E. used for calculating chemical exergies is that of Szargut.

According to Szargut, the chemical exergy of any substance is defined as the maximum work which can be obtained when the considered substance is brought in a reversible way to the state of the reference substances present in the reference environment.

Three kinds of reference substances can be accepted:

  • gaseous components of the atmospheric air
  • solid components of the external layer of the Earth's crust
  • ionic or molecular components of seawater

Szargut assumes the reference substances most common in the environment. Some authors select the most stable reference substances (Ahrendts 1980, Diederichsen 1991. However, sometimes the most stable substances are very rare in the natural environment, because their formation is kinetically blocked (for example, some nitrates).

Standard chemical exergy results from a conventional assumption of a standard ambient temperature and pressure and standard concentration of reference substances in the natural environment. The values of standard chemical exergy of chemical elements and compounds can be gathered in tables (see Table 1 below).

The standard chemical exergy of any chemical compound can be calculated by means of of the exergy balance of a reversible formion reaction, as in Eq. 1 :

Exergy

Where:

  • DGf formation Gibbs energy
  • ne amount of kmol of the element e
  • bchne standard chemical exergy of the element.

Download the complete methodology here.

Table 1: Chemical exergy of the Elements. Source: Szargut et al. 2005
Name Element bch (kJ/mol)
Silver Ag 69,85
Aluminium Al 796,10
Argon Ar 11,69
Arsenic As 493,83
Gold Au 59,88
Boron B 628,60
Barium Ba 776,76
Beryllium Be 604,53
Bismuth Bi 274,92
Bromine Br2 100,89
Carbon C 410,25
Calcium Ca 731,40
Cadmium Cd 293,38
Cerium Ce 1054,40
Chlorine Cl2 124,02
Cobalt Co 308,82
Chromium Cr 584,49
Cesium Cs 404,58
Copper Cu 134,25
Dysprosium Dy 975,35
Erbium Er 973,15
Europium Eu 1004,40
Fluorine F2 481,54
Iron Fe 376,99
Gallium Ga 514,75
Gadolinium Gd 970,22
Germanium Ge 556,35
Hydrogen H2 236,10
Helium He 30,37
Hafnium Hf 1061,28
Mercury Hg 115,00
Holmium Ho 979,54
Iodine I2 174,74
Indium In 437,60
Iridium Ir 256,56
Potash K 366,66
Kripton Kr 34,36
Lanthanum La 994,53
Lithium Li 393,03
Lutetium Lu 946,76
Magnesium Mg 629,37
Manganese Mn 496,42
Molybdenium Mo 730,27
Nitrogen N2 0,72
Sodium Na 336,71
Niobium Nb 900,29
Neodymium Nd 970,08
Neon Ne 27,16
Nickel Ni 232,71
Oxygen O2 3,97
Osmium Os 369,78
Phosphorous P 861,42
Lead Pb 232,41
Palladium Pd 146,00
Praseodymium Pr 964,04
Platinum Pt 140,97
Plutonium Pu 1099,87
Radium Ra 826,27
Rubidium Rb 388,89
Rhenium Re 560,56
Rhodium Rh 179,62
Rutenium Ru 318,45
Sulfur S 607,05
Antimonium Sb 438,02
Scandium Sc 923,89
Selenium Se 346,47
Silicon Si 854,10
Samarium Sm 994,23
Tin Sn 558,67
Strontium Sr 773,59
Tantalum Ta 974,81
Terbium Tb 999,40
Tellurium Te 329,10
Thorium Th 1220,67
Titanium Ti 906,65
Thalium Tl 194,16
Thulium Tm 952,50
Uranium U 1196,22
Vanadium V 721,45
Wolfram W 827,46
Xenon Xe 40,33
Ytrium Y 966,39
Yterbium Yb 944,85
Zinc Zn 339,25
Zirconium Zr 1080,88
Relevant bibliography on Reference Environments


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