The rate law for the reaction 2 NO2 Cl(g) ⟶2 NO2(g)+Cl2(g) (overall equation) is first order

step 1 In this problem, given reaction is 2 moles of nitrile chloride NO2 CL gives 2 moles of NO2 gas a

The rate law for the reaction 2 NO2 Cl(g) ⟶2 NO2(g)+Cl2(g) ...

The rate law for the reaction $$ 2 \mathrm{NO}_{2} \mathrm{Cl}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)+\mathrm{Cl}_{2}(g) \quad \text { (overall equation) } $$ is first order in nitryl chloride, $\mathrm{NO}_{2} \mathrm{Cl}$. $$ \text { Rate }=k\left[\mathrm{NO}_{2} \mathrm{Cl}\right] $$ Explain why the mechanism for this reaction cannot be the single elementary reaction $$ 2 \mathrm{NO}_{2} \mathrm{Cl} \longrightarrow 2 \mathrm{NO}_{2}+\mathrm{Cl}_{2} $$ (elementary reaction)

The rate law for the reaction
$$
2 \mathrm{NO}_{2} \mathrm{Cl}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)+\mathrm{Cl}_{2}(g) \quad \text { (overall equation) }
$$
is first order in nitryl chloride, $\mathrm{NO}_{2} \mathrm{Cl}$.
$$
\text { Rate }=k\left[\mathrm{NO}_{2} \mathrm{Cl}\right]
$$
Explain why the mechanism for this reaction cannot be the single elementary reaction
$$
2 \mathrm{NO}_{2} \mathrm{Cl} \longrightarrow 2 \mathrm{NO}_{2}+\mathrm{Cl}_{2}
$$
(elementary reaction)

Key Concepts

Reaction Mechanism

A reaction mechanism is a series of elementary steps that describe the pathway from reactants to products. In cases where the overall reaction's stoichiometry does not match the observed rate law, it implies that the true mechanism involves multiple steps. The discrepancy between the expected second-order rate law (from a single bimolecular step) and the observed first-order rate law suggests that the rate-determining step is not the simultaneous collision of two NO?Cl molecules, but likely involves a preliminary unimolecular decomposition or a fast pre-equilibrium step.

Molecularity

Molecularity refers to the number of reactant molecules involved in an elementary step. A unimolecular step involves one reactant molecule and results in a first-order rate law, whereas a bimolecular step involves two reactant molecules and leads to a second-order rate law. Since the observed reaction is first order, the rate-determining step must be unimolecular rather than bimolecular.

Elementary Reaction

An elementary reaction is one that occurs in a single step, and its rate law can be directly inferred from its stoichiometry. For a reaction written as 2NO?Cl ? 2NO? + Cl?, an elementary one-step process would typically have a rate law that is second order in NO?Cl, contradicting the observed first-order law.

Rate Law

The rate law expresses the dependency of the reaction rate on the concentrations of the reactants, determined empirically. In this case, the reaction is observed to be first order in nitryl chloride, meaning the rate is proportional to the concentration of NO?Cl raised to the power of one.

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