Spontaniety of gas(Nitrogen) adsorption over solid(Zeolite).

1. Jul 12, 2012

AbhiNature

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?