Solution
= Solution
For competing reactant and product species on shared equivalent sites, add each $b_jC_j$ term to the denominator:
$$
\theta_i=\frac{b_iC_i}{1+\sum_jb_jC_j}.
$$
Rapid product <desorption> makes product coverages small, reducing competitive site blocking and simplifying the rate to reactant coverage alone. Without that assumption, product <adsorption> can inhibit conversion and make the apparent rate evolve as products accumulate.