Equilibria and Related Problems

According to most early observations on insufficiently cleaned metal surfaces, chemisorption proceeds slowly and continues at a decreasing rate, for several days, so that final attainment of equilibrium is never fully assured. Usually, the adsorbed amounts were determined at a stage when the gas uptake had become very slow. As described in the foregoing sections, on clean metallic surfaces chemisorption comes to a definite endpoint without a slow drift. However, even in such cases it is important to 

Benton and White (35) established the adsorption equilibria of hydrogen on reduced nickel by approaching them from both higher and lower pressure at the upper part of the adsorption isotherm keeping the 

It will be shown later on the basis of statistical mechanics that the chemisorbed atoms are immobile in the sense that they are vibrating around the equilibrium position rather than undergoing two-dimensional translation. 

Two types of adsorption are usually postulated, the one being the physical adsorption which occurs at a lower temperature and is associated with smaller adsorption heats of the magnitude of the latent heat of evaporation of the adsorbate, and the other the chemical adsorption or chemisorption occurring usually at higher temperatures with larger heats of the magnitude of heats of chemical reactions. 

An interesting example of an isobar having two maxima at 80° and 218°C. has been reported in the case of zinc oxide-hydrogen by Taylor and Strother (39), and a similar one at —80° and 100°C. in the case of 

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