If the reaction NO2+CO ⟶NO+CO2 occured by a one-step collision process, what would be the expect

step 1 In this question, we have a given overall reaction, N -O -2 plus CO goes to N -O plus CO2. If th

If the reaction NO2+CO ⟶NO+CO2 occured by a one-step...

If the reaction $$\mathrm{NO}_{2}+\mathrm{CO} \longrightarrow \mathrm{NO}+\mathrm{CO}_{2}$$ occured by a one-step collision process, what would be the expected rate law for the reaction? The actual rate law is rate $=k\left[\mathrm{NO}_{2}\right]^{2}$. Could the reaction actually occur by a one-step collision between $\mathrm{NO}_{2}$ and CO? Explain.

Key Concepts

Elementary Reaction versus Mechanism

An elementary reaction involves a single collision step between reactant molecules and its rate law directly mirrors the stoichiometry (molecularity) of that collision. In this case, if the reaction occurred in one step between NO? and CO, the expected rate law would be rate = k[NO?][CO]. The discrepancy in the experimental rate law indicates that the reaction does not proceed as a simple one-step process, but rather through a more complex mechanism involving multiple steps.

Molecularity

Molecularity refers to the number of reactant species involved in an elementary step. A one-step bimolecular reaction would be expected to have a reaction order of one with respect to each reactant, resulting in a second-order overall rate law. The experimental observation that the rate law depends on the square of [NO?] suggests involvement of two NO? molecules, indicating that the slow or rate-determining step likely involves more than one NO? molecule.

Rate Law

The rate law provides the relationship between the concentrations of reactants and the reaction rate, reflecting the underlying reaction mechanism. For an elementary reaction, the rate law is predicted directly from the stoichiometry of the reactive collision, whereas for a complex mechanism, the experimentally observed rate law may differ from the overall stoichiometry.

Collision Theory

Collision theory describes reactions as occurring when reactant molecules collide with sufficient energy and proper orientation. In a single-step or elementary reaction, the reaction rate is proportional to the frequency of effective collisions among the reactant molecules. Since the actual rate law does not match the prediction from a direct collision between NO? and CO, it implies that the actual reaction mechanism involves additional steps or reactive intermediates that are not accounted for by a simple collision theory model.

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