In a database of solid microporous materials I have the Henry coefficient in units of $\pu{mol kg^{-1} Pa^{-1}}.$ How to convert to $\pu{Pa^{-1}}?$ I tried to multiply by the molar mass of the sorbate (in my case $\ce{H2O})$ expressed in $\pu{kg}$ (so $\pu{18.02E-3 kg mol^{-1}}),$ but it turns out the same result of having a gas as solute and the water as solvent according to Sander [1].


  1. Sander, R. Compilation of Henry’s Law Constants (Version 4.0) for Water as Solvent. Atmos. Chem. Phys. 2015, 15 (8), 4399–4981. DOI: 10.5194/acp-15-4399-2015. (PDF)
  • $\begingroup$ You wrote "How to convert in Pa$^{−1}$?" To what units? $\endgroup$
    – AChem
    Jun 25, 2021 at 19:55
  • $\begingroup$ Sorry, I mean "how to convert $\pu{mol kg^{-1} Pa^{-1}}$ to $\pu{Pa^{-1}}$?" $\endgroup$
    – Gio
    Jun 25, 2021 at 20:39
  • 1
    $\begingroup$ You cannot. How will you eliminate mol and kg? $\endgroup$
    – AChem
    Jun 25, 2021 at 20:42
  • $\begingroup$ What is your initial unit of Henry's constant and what is your desired unit? $\endgroup$
    – AChem
    Jun 25, 2021 at 20:44
  • $\begingroup$ I think you are confusing adsorbent and adsorbate (which you call "sorbate"). If water is adsorbing into the solid it is the adsorbate. The Henry's law constant allows you to convert between vapor pressure of adsorbate (water) and its concentration (as moles of water per kg of microporous material) in the adorbent (microporous material). $\endgroup$
    – Buck Thorn
    Jun 26, 2021 at 5:44