Why is it unlikely that the reaction \(\mathrm{A}+2 \mathrm{~B}+\mathrm{C} \rightarrow \mathrm{P}\) occurs in one step?

For a reaction to occur in a single step, all the reactants involved in the reaction must collide simultaneously and with the correct orientation to form bonds. Molecularity refers to the number of reactant particles involved in an elementary step of the overall reaction. In this reaction, three reactant particles A, B, and C are involved in forming the product P. Since there are three reactant particles, the molecularity of the reaction is 3. It's essential to consider if it's highly probable for all three reactants to collide and bond simultaneously.

The probability of a three-particle collision is generally considered low. This is because, for this reaction to occur in a single step, the three reactant particles must come together and collide simultaneously with the correct orientation to form the product. Such a simultaneous collision requires a high level of precise coordination among the reactants and is, therefore, considered improbable in chemical kinetics.

In reactions where the molecularity is greater than 2 (i.e., more than two particles are involved), it is often found that they typically occur via a sequence of simpler elementary steps. These steps occur sequentially, involving fewer reactants (usually one or two) in each step. Considering the improbability of a three-particle collision, it is more likely that the given reaction proceeds through a series of elementary steps involving two or fewer reactants. This results in an overall reaction mechanism that is more feasible in terms of collision theory and chemical kinetics. In conclusion, it is unlikely that the reaction A + 2B + C → P occurs in one step due to the low probability of a three-particle collision and the requirement for precise coordination. Reactions with more than two reactants typically proceed through a sequence of simpler elementary steps involving fewer reactant particles.