Nitryl bromide, NO2 Br, decomposes into nitrogen dioxide and...

Nitryl bromide, $\mathrm{NO}_{2} \mathrm{Br}$, decomposes into nitrogen dioxide and bromine. $$ 2 \mathrm{NO}_{2} \mathrm{Br}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)+\mathrm{Br}_{2}(g) $$ A proposed mechanism is $$ \begin{array}{r} \mathrm{NO}_{2} \mathrm{Br} \longrightarrow \mathrm{NO}_{2}+\mathrm{Br} \\ \mathrm{NO}_{2} \mathrm{Br}+\mathrm{Br} \longrightarrow \mathrm{NO}_{2}+\mathrm{Br}_{2} \end{array} $$ Write the rate law predicted by this mechanism.

Nitryl bromide, $\mathrm{NO}_{2} \mathrm{Br}$, decomposes into nitrogen dioxide and bromine.
$$
2 \mathrm{NO}_{2} \mathrm{Br}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)+\mathrm{Br}_{2}(g)
$$
A proposed mechanism is
$$
\begin{array}{r}
\mathrm{NO}_{2} \mathrm{Br} \longrightarrow \mathrm{NO}_{2}+\mathrm{Br} \\
\mathrm{NO}_{2} \mathrm{Br}+\mathrm{Br} \longrightarrow \mathrm{NO}_{2}+\mathrm{Br}_{2}
\end{array}
$$
Write the rate law predicted by this mechanism.

Key Concepts

Reaction Intermediates

Reaction intermediates are transient species formed during the stepwise process of a reaction mechanism. They do not appear in the overall balanced equation but are crucial for understanding how reactants are converted into products. Their detection and theoretical treatment, such as through the pre-equilibrium or steady-state approximations, are essential for linking the mechanism to the observed kinetics.

Pre-equilibrium Approximation

The pre-equilibrium approximation is used when an early step in the mechanism establishes a rapid equilibrium between reactants and an intermediate. Under this approximation, the concentration of the intermediate can be expressed in terms of the concentrations of the reactants using the equilibrium constant, which is then substituted into the rate law of the subsequent, slower step.

Rate Law

The rate law is an expression that relates the rate of a chemical reaction to the concentrations of the reactants raised to specific powers, which are the reaction orders. It is derived from the elementary steps of a reaction mechanism and is fundamental in connecting kinetic observations with the underlying molecular events of the reaction.

Reaction Mechanism

A reaction mechanism outlines the step-by-step sequence of elementary reactions by which an overall chemical change occurs. It helps in understanding how bonds are broken and formed and provides insights into the formation and consumption of intermediates, leading to the overall transformation observed in the reaction.

Rate-Determining Step

The rate-determining step is the slowest step in a reaction mechanism that controls the overall reaction rate. Since it is the bottleneck, the rate law of the slow step often largely dictates the form of the overall rate law, requiring careful analysis to connect the mechanism to observable kinetics.

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