Partial molal entropies of argon and nitrogen have been determined in the temperature range 173 to 273 °K for the systems argon in Li-, Na-, K -, Ca-, Sr- and Ba-faujasite and nitrogen in Li-, Na- and K -faujasite, over the degrees of saturation, θ, of the intracrystalline free volume of approximately 0< θ 2 in K-faujasite) the entropy data indicate substantial intracrystalline mobility. When the systems exhibit energetic heterogeneity, this is associated with the presence of cations of high polarizing power and smaller ionic radius, but not all the cations of a given kind contribute equally to the effects observed. Accordingly, the energetic heterogeneity tends to disappear rather rapidly with increasing charge of gas, while at the same time the thermal entropy rises. This change in thermal entropy has been interpreted as due to increased rotational freedom (N 2 ) and to increased amplitudes of vibration (N 2 and A) as molecules become increasingly located in less energetically sorbing regions of the intracrystalline capillary system.