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Title: The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

Abstract

The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate ions H{sub 3}PO{sub 4}{sup 0}(aq), H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), or PO{sub 4}{sup 3-}(aq). Many divalent, trivalent, and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation requires comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier; with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H{sub 2}PO{sub 4}{sup -}(aq) and HPO{sub 4}{sup 2-}(aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ {center_dot} mol{sup -1} per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations.more » In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), and PO{sub 4}{sup 3-}(aq) ions at 298.15 K and p{sup o} = 1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S{sub m}{sup o}(H{sub 2}PO{sub 4}{sup -}, aq, 298.15 K) = 90.6 {+-} 1.5 J {center_dot} K{sup -1} mol{sup -1} was obtained.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
920864
Report Number(s):
UCRL-JRNL-227692
Journal ID: ISSN 0095-9782; JSLCAG; TRN: US200805%%215
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solution Chemistry, vol. 36, no. 11/12, October 30, 2007, pp. 1585-1599; Journal Volume: 36; Journal Issue: 11/12
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ATOMS; CHEMICAL ENGINEERING; CHEMISTRY; EVALUATION; ORIGIN; PHOSPHATES; PHOSPHORUS; RECOMMENDATIONS; SIMULATION; SOLUBILITY; THERMODYNAMIC PROPERTIES; THERMODYNAMICS

Citation Formats

Rard, J A, and Wolery, T J. The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA. United States: N. p., 2007. Web. doi:10.1007/s10953-007-9205-7.
Rard, J A, & Wolery, T J. The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA. United States. doi:10.1007/s10953-007-9205-7.
Rard, J A, and Wolery, T J. Tue . "The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA". United States. doi:10.1007/s10953-007-9205-7. https://www.osti.gov/servlets/purl/920864.
@article{osti_920864,
title = {The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA},
author = {Rard, J A and Wolery, T J},
abstractNote = {The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate ions H{sub 3}PO{sub 4}{sup 0}(aq), H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), or PO{sub 4}{sup 3-}(aq). Many divalent, trivalent, and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation requires comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier; with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H{sub 2}PO{sub 4}{sup -}(aq) and HPO{sub 4}{sup 2-}(aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ {center_dot} mol{sup -1} per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), and PO{sub 4}{sup 3-}(aq) ions at 298.15 K and p{sup o} = 1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S{sub m}{sup o}(H{sub 2}PO{sub 4}{sup -}, aq, 298.15 K) = 90.6 {+-} 1.5 J {center_dot} K{sup -1} mol{sup -1} was obtained.},
doi = {10.1007/s10953-007-9205-7},
journal = {Journal of Solution Chemistry, vol. 36, no. 11/12, October 30, 2007, pp. 1585-1599},
number = 11/12,
volume = 36,
place = {United States},
year = {Tue Jan 30 00:00:00 EST 2007},
month = {Tue Jan 30 00:00:00 EST 2007}
}
  • This review critically evaluates the reported thermodynamic data on chromium metal, oxides, hydroxides, free aqueous ions, and hydrolysis species. Several discrepancies and inconsistencies have been uncovered and resolved to improve equilibrium calculations for chemical modeling and related engineering purposes. A revised set of data is derived from evaluation of electrochemical measurements, silver chromate solubility measurements, and auxiliary post-1980 data, reevaluation of earlier data, and reconsideration of the path for the thermodynamic network. The recommended thermodynamic values for Cr{sub (cr)}, Cr{sub (aq)}{sup 2+}, Cr{sub (aq)}{sup 3+}, CrO{sub 4(aq)}{sup 2{minus}}, Cr{sub 2}O{sub 7(aq)}{sup 2{minus}}, Cr{sub 2}O{sub 3(cr)}, CrO{sub 3(cr)}, FeCr{sub 2}O{sub 4(cr)},more » CrCl{sub 2(cr)}, CrCl{sub 3(cr)}, and KFe{sub 3}(CrO{sub 4}){sub 2}(OH){sub 6(cr)} at 25 C, 1 bar, and infinite dilution are given. 140 refs.« less
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