which is consistent with the relationship between selectivity and Henry's constant at lowpressure. According to Hess's law, the exchange enthalpy is the difference between the adsorption enthalpies ∆ exc 𝐻 A/B = ∆ ads 𝐻 A -∆ ads 𝐻 B . Finally, the entropic term -𝑇 𝑆 derives from the exchange equilibrium -𝑇 ∆ exc 𝑆 = ∆ exc 𝐺 -∆ exc 𝐻. We use these formulas to calculate the Gibbs free energy of the most influential descriptor, the xenon/krypton exchange equilibrium at infinite dilution ∆𝐺 Xe/Kr 0 and most of the energy descriptors presented in Table .