THE RUDOLF REPORT

6. FORMATION AND STABILITY OF IRON BLUE6.5.4.2. ExcursusThere are two more steps in the observed reaction which could,theoretically, have an influence on the reaction under consideration:A) Adsorption on the solid material;B) Dissociation of hydrogen cyanide.A: The adsorption of hydrogen cyanide on solid surfaces decreaseswith rising temperature, according to Langmuire (see Graph3). 352 KT · p · e-∆H/RTΘ =1- K (1)T · p · e-∆H/RTΘ = Degree of adsorption ∆H = adsorption enthalpy (negative)K = variableR = universal gas constantT = temperature e = Euler’s number (2.71828...)p = gas pressure120100degree of coverage [%]806040200temperatureGraph 3: Degree of coverage of the surface of a solidmaterial with an adsorbed gas as a function of temperature(schematic)The intensity of the decrease of the equilibrium degree of adsorption(coverage) with rising temperature as well as the point of approximatesaturation, however, are unknown for the problem at hand.But since, as discussed before, all reactions under consideration requireaqueous solutions anyway, adsorptions on solid, i.e., dry surfaces are352 J. Oudar, Physics and Chemistry of Surfaces, Blackie & Son, Glasgow 1975, pp. 26ff.167