The total number of species defined in the homogeneous system is

(8–153)

where is the number of gas-phase species; and is the number of surface- and bulk-phase species on the m th material; and is the total number of different reacting materials defined in the reactor. The maximum number of unknowns in the problem, , is therefore given by

(8–154)

where, in addition to species fractions and surface phase densities, we will be solving L additional equations, which may include gas temperature, electron temperature, and/or surface temperature. These equations are solved simultaneously for all reactors in the cluster. The equation corresponding to gas-phase species is Equation 8–1 . The equation corresponding to surface phase site fractions is Equation 8–9 , while the equation for bulk species is either Equation 8–19 or Equation 8–20 , depending on whether or not the bulk species may be etched. The equations corresponding to site densities, in the case when non-site-conserving reactions are included in the surface mechanism, is Equation 8–21 . The gas temperature is determined by Equation 8–147 and the electron energy equation is Equation 8–141 .