Project Details Henry’s law constants

Project No.:
Start Date:
07 October 2019
End Date:


Henry’s law describes the distribution of chemicals between the gas and the aqueous phase. There is a plethora of ways to define a corresponding equilibrium constant. This has led to many inconsistent and ambiguous definitions, units, and names in the literature. Unfortunately, the recommendations in miscellaneous IUPAC publications are also incompatible. As an outcome of this project, a well-defined set of recommendations to clear-up these incompatibilities will be provided.


Current IUPAC recommendations: The Gold Book has a page about Henry’s law but does not define a Henry’s law constant ( Instead, a “rational solubility coefficient” is defined as a/p (activity/fugacity). The Green book uses a lower case k as the symbol for the Henry’s law constant and defines it as f/x (fugacity/amount fraction). The introduction to the IUPAC-NIST Solubility Data Series by Sazonov and Shaw uses an upper case K as the symbol and defines the Henry’s law constant as p/x (pressure/amount fraction). Alternative definitions (K2 = p/c and Kc = c/c) are also briefly mentioned. The IUPAC Recommendations “Glossary of atmospheric chemistry terms” by Calvert use the symbol H and the definition c/p (concentration/pressure). The book “Chemicals in the Atmosphere: Solubility, Sources and Reactivity” by Fogg & Sangster is internally inconsistent. It uses several symbols and several different definitions in different chapters of the book.

Previous work already done on the proposed project: A compilation of 17350 values of Henry’s law constants for 4632 species, collected from 689 references, has been published ( Online access to the searchable database is available at

Work to do:
1. Create a list that shows the usage (i.e., nomenclature, symbols, and units) of Henry’s law constants in publications by miscellaneous research communities.
2. Create a set of definitions for all variants of the Henry’s law constant that appear in the literature.
3. Create an internally consistent and unambiguous system for nomenclature and symbols.
4. Discuss which variants should be recommended, and which should be either tolerated or deprecated.


Project announcement published in Chem Int Jan 2020, p. 29

January 2021 – The provisional recommendation titled “HENRY’S LAW CONSTANTS” is available for comments till 31 May 2021 > see

Page last update 1 Feb 2021