Gas Adsorption on Solid Surfaces Langmuir Theory

This equation assumes that only one layer of gas molecule adsorbs. A monolayer of gas adsorbs in the following case there are only a given number of adsorption sites for only a monolayer. This is the most simple adsorption model. The amount adsorbed, N, is related to the monolayer coverage, Ns , as follows  

From the experimental data, one can plot p/N versus p. The plot will be linear, and the slope is equal to 1/Nsn,. The intersection gives the value of a. Charcoal is found to adsorb 15 mg of N2 as monolayer. Another example is that of adsorption of N2 on mica surface (at 90 K). The following data were found  

That the adsorbed molecules are stable after adsorption 

The surface area of the soUd can be estimated from the plot of p/N versus p. Most data fit this equation under normal conditions and are therefore widely applied to analyze adsorption process. Langmuir adsorption is found for the data of nitrogen on mica (at 90K). The data were found to be as follows  

This shows that the amount of gas adsorbed increases by a factor 28/24 = 1.2 when the gas pressure increases twofold. 

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