Question

In reaction CFCl3 + UV Light -> CFCl2 + Cl, there is only one reactant (CFCl3) and no collision

Answer 1

The reaction CFCl3 + UV Light -> CFCl2 + Cl does not need another reactant as with CFCl3 because the reaction itself is reactive to light. Note that there are reactions that are sensitive to light to form products and when this type of reaction are not exposed to light, no reaction occurs.