Que peut-on dire quant au caractère simple (une seule étape)...

Que peut-on dire quant au caractère simple (une seule étape) ou complexe (plus d'une étape) des réaction suivantes ? Pour celles qui comportent plus d'une étape, proposez un mécanisme plausible en accord avec leur loi de vitesse. a) $\mathrm{NO}_2+\mathrm{CO}=\mathrm{NO}+\mathrm{CO}_2$ $$ v=k c^2\left(\mathrm{NO}_2\right) $$ b) $\mathrm{SO}_2 \mathrm{Cl}_2=\mathrm{SO}_2+\mathrm{Cl}_2$ $$ v=k c\left(\mathrm{SO}_2 \mathrm{Cl}_2\right) $$ c) $\mathrm{CH}_3 \mathrm{Cl}+\mathrm{HO}^{-}=\mathrm{CH}_3 \mathrm{OH}+\mathrm{Cl}^{-}$ $$ v=k \mathrm{c}\left(\mathrm{CH}_3 \mathrm{Cl}\right) \mathrm{c}\left(\mathrm{HO}^{-}\right) $$ d) $2 \mathrm{NO}_2 \mathrm{Cl}=2 \mathrm{NO}_2+\mathrm{Cl}_2$ $$ v=k \mathrm{c}\left(\mathrm{NO}_2 \mathrm{Cl}\right) $$ e) $2 \mathrm{NO}_2+\mathrm{O}_3=\mathrm{N}_2 \mathrm{O}_5+\mathrm{O}_2$ $$ v=k \mathrm{c}\left(\mathrm{NO}_2\right) \mathrm{c}\left(\mathrm{O}_3\right) $$ f) $\mathrm{CH}_3 \mathrm{COCH}_3+\mathrm{Br}_2+\mathrm{HO}^{-}=$ $$ \mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{Br}+\mathrm{H}_2 \mathrm{O}+\mathrm{Br}^{-} \quad v=k \mathrm{c}\left(\mathrm{CH}_3 \mathrm{COCH}_3\right) \mathrm{c}\left(\mathrm{HO}^{-}\right) $$ g) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Cl}+\mathrm{HO}^{-}=$ $$ \mathrm{CH}_2=\mathrm{CH}_2+\mathrm{H}_2 \mathrm{O}+\mathrm{Cl}^{-} \quad v=k \mathrm{c}\left(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Cl}\right) \mathrm{c}\left(\mathrm{HO}^{-}\right) $$

Que peut-on dire quant au caractère simple (une seule étape) ou complexe (plus d'une étape) des réaction suivantes ? Pour celles qui comportent plus d'une étape, proposez un mécanisme plausible en accord avec leur loi de vitesse.
a) $\mathrm{NO}_2+\mathrm{CO}=\mathrm{NO}+\mathrm{CO}_2$
$$
v=k c^2\left(\mathrm{NO}_2\right)
$$
b) $\mathrm{SO}_2 \mathrm{Cl}_2=\mathrm{SO}_2+\mathrm{Cl}_2$
$$
v=k c\left(\mathrm{SO}_2 \mathrm{Cl}_2\right)
$$
c) $\mathrm{CH}_3 \mathrm{Cl}+\mathrm{HO}^{-}=\mathrm{CH}_3 \mathrm{OH}+\mathrm{Cl}^{-}$
$$
v=k \mathrm{c}\left(\mathrm{CH}_3 \mathrm{Cl}\right) \mathrm{c}\left(\mathrm{HO}^{-}\right)
$$
d) $2 \mathrm{NO}_2 \mathrm{Cl}=2 \mathrm{NO}_2+\mathrm{Cl}_2$
$$
v=k \mathrm{c}\left(\mathrm{NO}_2 \mathrm{Cl}\right)
$$
e) $2 \mathrm{NO}_2+\mathrm{O}_3=\mathrm{N}_2 \mathrm{O}_5+\mathrm{O}_2$
$$
v=k \mathrm{c}\left(\mathrm{NO}_2\right) \mathrm{c}\left(\mathrm{O}_3\right)
$$
f) $\mathrm{CH}_3 \mathrm{COCH}_3+\mathrm{Br}_2+\mathrm{HO}^{-}=$
$$
\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{Br}+\mathrm{H}_2 \mathrm{O}+\mathrm{Br}^{-} \quad v=k \mathrm{c}\left(\mathrm{CH}_3 \mathrm{COCH}_3\right) \mathrm{c}\left(\mathrm{HO}^{-}\right)
$$
g) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Cl}+\mathrm{HO}^{-}=$
$$
\mathrm{CH}_2=\mathrm{CH}_2+\mathrm{H}_2 \mathrm{O}+\mathrm{Cl}^{-} \quad v=k \mathrm{c}\left(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Cl}\right) \mathrm{c}\left(\mathrm{HO}^{-}\right)
$$

Key Concepts

Molecularity

Molecularity describes the number of molecules that participate in a single elementary reaction step, such as unimolecular, bimolecular, or termolecular processes. It provides insight into the nature of elementary steps, establishing a direct correlation between the number of reactant encounters and the form of the rate law for elementary reactions.

Rate-Determining Step

In multi-step mechanisms, the rate-determining step is the slowest step that controls the overall reaction rate. This step acts as a bottleneck, and its kinetics heavily influence the overall rate law. Identifying the rate-determining step is crucial for constructing accurate and plausible mechanistic pathways.

Elementary Reactions

Elementary reactions are single?step processes in which the reaction occurs in one concerted event, with the rate law directly reflecting the stoichiometry of the reactants involved. In these processes, the observed kinetic order is the same as the number of reactant molecules colliding in that step, providing a direct link between the mechanism and the rate law.

Reaction Mechanism

A reaction mechanism details the step?by?step sequence of elementary processes by which overall chemical change occurs. In complex reactions, several intermediate steps are involved, and the overall reaction rate is determined by the interplay and speed of these individual steps, rather than by the overall stoichiometric equation.

Rate Law

The rate law is an expression that shows how the speed of a reaction depends on the concentration of its reactants, typically in the form v = k [A]^m[B]^n. The exponents m and n indicate the orders of reaction with respect to each reactant and, when deduced experimentally, provide critical clues about the molecular events and steps in the reaction mechanism.

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