2: Consider chemical adsorption and desorption kinetics in which the adsorption is via a physisorbed precursor state, but the desorption is directly from the chemisorbed state into the gas phase. The kinetics is described by the reaction chain, A(g)+SKdKaA:S(physi)KaA:S(chemi)KdA(g)+S where Ka (SI units of m3s1 ) is the second-order rate coefficient for adsorption of a gas phase atom into the physisorbed surface state, Kd(SI units of s 1 ) is the first order rate coefficient for desorption of a physisorbed atom into the gas phase, Kd is the second-order rate coefficient for adsorption of a physisorbed atom into the chemisorbed surface state, and Kd (SI units of s1 ) is the firstorder rate coefficient for desorption of a chemisorbed atom directly into the gas phase. Assume a surface density of n0 for both physisorption and chemisorption sites, and let be the surface coverage for physisorption and be the surface coverage for chemisorption. You may assume that because the physisorption sites lie above the chemisorption sites on the surface, a physisorption site can be located over either an empty or an occupied chemisorption site. 2.1 Write the site balance equation for physisorbed atoms in the steady state. From this show that the rate of chemisorption is, a=KanAS+Kd+Kan0(1)KaKanAsn02(1) HINT: Pay particular attention to the units of the rate coefficients. 2.2 Write the site balance equation for chemisorbed atoms in the steady state. Using this and your result in 2.1 , find the equation to determine (there is no need to solve it)