The reaction of NO2(g) and CO(g) is thought to occur in two steps: Step 1 Slow NO2(g)+NO2(g) ⟶

step 1 There are several parts of this question. Firstly, we're trying to determine that the different

The reaction of NO2(g) and CO(g) is thought to occur in two...

The reaction of $\mathrm{NO}_{2}(\mathrm{g})$ and $\mathrm{CO}(\mathrm{g})$ is thought to occur in two steps: Step 1 Slow $\quad \mathrm{NO}_{2}(\mathrm{g})+\mathrm{NO}_{2}(\mathrm{g}) \longrightarrow \mathrm{NO}(\mathrm{g})+\mathrm{NO}_{3}(\mathrm{g})$ Step 2 Fast $\quad \mathrm{NO}_{3}(\mathrm{g})+\mathrm{CO}(\mathrm{g}) \longrightarrow \mathrm{NO}_{2}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})$ (a) Show that the elementary steps add up to give the overall, stoichiometric equation. (b) What is the molecularity of each step? (c) For this mechanism to be consistent with kinetic data, what must be the experimental rate equation? (d) Identify any intermediates in this reaction.

The reaction of $\mathrm{NO}_{2}(\mathrm{g})$ and $\mathrm{CO}(\mathrm{g})$ is thought to occur in two steps:
Step 1 Slow $\quad \mathrm{NO}_{2}(\mathrm{g})+\mathrm{NO}_{2}(\mathrm{g}) \longrightarrow \mathrm{NO}(\mathrm{g})+\mathrm{NO}_{3}(\mathrm{g})$
Step 2 Fast $\quad \mathrm{NO}_{3}(\mathrm{g})+\mathrm{CO}(\mathrm{g}) \longrightarrow \mathrm{NO}_{2}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})$
(a) Show that the elementary steps add up to give the overall, stoichiometric equation.
(b) What is the molecularity of each step?
(c) For this mechanism to be consistent with kinetic data, what must be the experimental rate equation?
(d) Identify any intermediates in this reaction.

Key Concepts

Reaction Mechanism

A reaction mechanism is the sequence of elementary steps by which an overall chemical reaction occurs. Each elementary step represents a single molecular event with its own rate law, and when these steps are added together (with cancellation of any intermediates), they yield the overall balanced reaction. Understanding the mechanism helps in linking the overall stoichiometric equation with the kinetics observed experimentally.

Elementary Reaction Steps

Elementary reaction steps are the individual processes that occur in one collision or event. Their rate laws can be directly written from their stoichiometric equations, reflecting how the reactant molecules collide. In a mechanism, each step is assumed to occur as written, without any hidden complex pathways, and these steps add up to give the complete reaction.

Molecularity

Molecularity is a concept that describes the number of molecules or ions that participate as reactants in an elementary step. It is determined by the stoichiometry of that particular step. For example, a bimolecular reaction involves two reactant molecules colliding to form products. Each elementary step in a mechanism has its own molecularity, which determines its intrinsic rate law.

Rate-Determining Step

The rate-determining step is the slowest step in a multistep reaction mechanism, and it limits the overall rate of the reaction. Since it is the bottleneck, the rate law for the overall reaction is typically governed by this step. Other faster steps are assumed to occur almost instantaneously relative to the rate-determining step.

Rate Law/Experimental Rate Equation

The rate law expresses how the speed of a reaction depends on the concentration of the reactants. For a reaction mechanism, the experimentally measured rate law must be consistent with the kinetics of the rate-determining step. This means that even though the overall reaction may have a different stoichiometry, the observed rate law typically reflects the molecularity and rate constant of the slowest, rate-limiting step.

Reaction Intermediates

Reaction intermediates are species that are formed in one elementary step and consumed in a subsequent step, and they do not appear in the overall balanced equation. Although they are transient and typically present in very low concentrations, intermediates play a critical role in the progression of the reaction from reactants to products and are important in understanding the mechanism.

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