What is the molecularity of a reversible reaction?
For the reaction $$\ce {A &lt;=&gt; B + C}$$
its molecularity is unimolecular. If we were given $$\ce{B + C &lt;=&gt; A}$$ 
Its molecularity would be bimolecular. Thus we see molecularity is dependent on the number of reactant particles, even if it's in equilibrium.