Hello! The other day I was reading about adsorption(gas over solid), and there it stated that it is a spontaneous process. I wanted to know how spontaneous the process is. I therefore took nitrogen adsorption over zeolite as a candidate to find its spontaneity, and to my surprise, my calculations showed it to be a non-spontaneous process. I guess I am wrong somewhere, but I just cannot find where. Following are the calculations that I did; dG = dH - T*dS Assuming adsorption to be equivalent to converting gas to liquid. Therefore, dH = Heat of vaporization of Nitrogen = -5560J/mole T = 300K (Adsorption at 300K). S1 = Entropy of Nitrogen at 300K = 192J/moleK. S2 = Entropy of Nitrogen in liquid form (I did not find entropy data of liquid Nitrogen, but I did find data at 100K) = 160J/moleK. Which gives, dG = 4040J/mole - non-spontaneous. I saw a graph which showed quite a lot of adsorption at 300K. I speculate that, adsorption needs pressure and the source of this pressure has more than enough negative dG? Could you please help me understand this? Thanks!