Arsenic Thermodynamic Data

Italicized terms in the text of this appendix or words derived from the italicized terms are defined in the glossary of Appendix B. 

Not all published and widely accepted thermodynamic values are reliable. Nordstrom and Archer (2003) provide a detailed review of the controversies, uncertainties, and problems related to thermodynamic data for arsenic and its compounds and aqueous species. Many of the data are contradictory and the methods that produce the data are sometimes questionable or have not been thoroughly documented. Too often, data in the literature have been passed from reference to reference without critical evaluations. Some of the data have high measurement errors, were produced under undefined or poorly defined laboratory conditions, and involved unrepresentative sampling (Matschullat 2000, 298 Nordstrom and Archer, 2003). Furthermore, other questionable data originate from obscure documents or are written in languages that many individuals cannot read and properly interpret. Therefore, thermodynamic results must be accepted with a certain amount of caution. The table in this appendix includes thermodynamic data from various sources, which provide users with some idea of their variability. Although sometimes unavoidable, users 

Arsenic Edited by Kevin R. Henke 2009 John Wiley Sons, Ltd. ISBN 978-0-470-02758-5 

Chemical species Phase Temperature (K) Gibbs free energy (G ) (kj mol-1) Enthalpy (Hi) (kj mol-1) Entropy (5)) (J mol-1-K-1) Heat Capacity (Cpi) (J mol-1-K-1) Reference 

As(0) (elemental arsenic, rhombohedral or gray ) xls 298.15 0 0 35.6 Naumov, Ryzhenko and Khodakovsky (1974) 

---

Nordstrom, D.K. and Archer, D.G. (2003) Arsenic thermodynamic data and environmental geochemistry, in Arsenic in Ground Water (eds A.H. Welch and K.G. Stollenwerk), Kluwer Academic Publishers, Boston, MA, pp. 1-25. 

---