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The dependences of the differential molar isosteric heat of adsorption and entropy of adsorption of CO 2 on zeolite NaX were determined in wide temperature (196-423 K) and pressure (0.1 Pa to 5.4 MPa) intervals. In the initial region of adsorption (a < 1 mmol g -1 ), the differential molar heat of adsorption increases from 40 to 43 kJ mol -1 and then decreases to 33 kJ mol -1 . The heat of adsorption remains virtually unchanged at 3 mmol g -1 < a < 6.5 mmol g -1 and decreases sharply at high fillings of zeolite micropores (а > 7 mmol g -1 ). The heat of adsorption was found to be temperature dependent. The region with the constant heats shrinks with the temperature increase, and the heats begin to decrease at lower fillings of micropores. The dependences of the change in the differential entropy of the adsorption system on the amount adsorbed were calculated at different temperatures. The specific features of the behavior of the thermodynamic functions of this adsorption system in the initial and medium region of fillings are associated with interactions of adsorbate molecules with Na + cations and walls of large cavities. For high fillings, an increase in repulsion forces between adsorbed molecules results in a sharp expansion of the adsorbent and a decrease in the heat of adsorption.Investigation of the physical adsorption of gases and vapors in wide intervals of pressures and temperatures is important for the development of the theory of adsorp tion and industrial innovations.The use of a microporous crystalline adsorbent (zeo lite) as an object of studies makes it possible to avoid errors in determination of the adsorbent volume, which is especially significant for measuring adsorption in a region of high pressures.It has been shown previously 1 for the Хе-zeolite NaX system that a combination of adsorption data with results of adsorbent deformation allows one to introduce proper corrections in calculations of the thermodynamic charac teristics of an adsorption system. For instance, the isosteric heat of adsorption is described, in the general form, by the Bakaev equation 2where R is the universal gas constant; Z = pv g /(RT ) is the compressibility factor; p and v g are the pressure and spe cific volume of the equilibrium phase, respectively; v 1 = V 1 /m 0 is the specific reduced volume of the adsorp tion system; a = N a /m 0 is the absolute amount adsorbed;V 1 is the volume of a crystal with micropores; N a is the amount of the adsorbate in micropores; m 0 is the weight of the degassed adsorbent. If adsorption is not accompanied by sorbent deforma tion (v 1 ≠ f(a, T )), thenThe value of the second term is usually low (<1%) and becomes significant at high pressures 3 (р > 8-10 MPa). Therefore, at standard pressures (р < 100 kPa, Z = 1), expression (2) takes the formIn Fig. 1, solid curves are used to show the isosteric heats of adsorption of Хе on zeolite NaX calculated by Eq. (1) and dotted lines to show the heats calculated by Eq. (3). Comparing curves 5-7 and 5´-7´, one can see that the differences betw...