An example of a problem where there is severe counter-diffusion of the products is the deposition of SiO2 from tetraethoxysilane (TEOS) on a solid substrate

An example of a problem where there is severe counter-diffusion of the products is the deposition of SiO2 from tetraethoxysilane (TEOS) on a solid substrate. The reaction is represented as SiO(C2H5)4(g) → SiO2(s) + 4C2H4(g) + 2H2O(g) Note that 6 moles have to counter-diffuse and hence this retards mass transfer unless the mole fraction of TEOS is small. Consider deposition from a gas at a temperature of 400 K and pressure 0.1 atm and a mole fraction of TEOS of 0.2. The diffusivity is 0.1 cm2/s. Calculate the rate of reaction and the film growth rate assuming that the surface reaction is very rapid.