All blue fields allow input; press <RETURN> to calculate.

In the form below: some fields allow input, some do not. Press RETURN to recalculate results. Values of read-only fields will be recalculated than. You might not be extra informed about the changes.



This calculator gets an estimate of the chemical potential of the molecules (atoms in case of “½ H2” and “½ O2”) as required for so-called ab-initio thermodynamics or calculating adsorption/desorption equilibria in surface physics. It assumes an ideal gas, but it does not care whether the substance would exist as a gas under the given conditions. In case of doubt, use the Vapor Pressure Calculator to make sure.

For molecules not included in this calculator, the enthalpy H and entropy S per molecule can be calculated for a given temperature by the TPD Calculator (select “Calculation for: T_peak given”); the chemical potential is then given by μ = HTS.

Data sources:
Based on M. W. Chase, NIST-JANAF Thermochemical Tables. Journal of Physical and Chemical Reference Data Monograph 9 (American Chemical Society &amp; American Institute of Physics for the National Institute of Standards and Technology; Washington, D.C. & Woodbury, N.Y., 1998), using parametrization (Shomate Equation) from, opens an external URL in a new window.
Equations: K. Reuter and M. Scheffler, Phys. Rev. B 65, 035406 (2001) [Erratum in Phys. Rev. B 75, 049901 (2007)].

Copyright © by Michael Schmid, IAP/TU Wien Surface Physics Group 2013–2024. No warranty for correctness of results.