Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

2 THE SOLID-GAS INTERFACE 195The reaction order (x) for desorption can readily be determined from thepressure-time curve. This is best demonstrated by considering that the rate of lossof gas from the cell is negligible during the desorption, thenwherewhereANANmx=2, -- -n(t,)Xl+n(t,)XFor a hyperbolic heating curve i.e. 1/T = a+bt= C(exp [Bt] - 1)Evolution curves for k st and second order desorption are shown in Fig. 7. Theydiffer qualitatively in shape and their dependence on the initial concentration ofFig. 7. Dependence of evolution curve on rate law for desorption. First order versus second orderdesorption; ED = 80 kcal. mole-'; vi = 3.54 x 1Ola sec-l; Y, = 8 x molecules-1. sec-'.cm*.For variable heat, ED = Ei-~n; ED" = 80 kcal. mole-'; 7 = 0.3 kcal. mole-' per 101smolecdes.cm-*. From ref. 88.References pp. 270-278