Question

In the following reaction sequence for the catalytic formation of ozone from molecular oxygen, which chemical compound is the catalyst: nitrogen monoxide or nitrogen dioxide? $$ \begin{aligned} &\mathrm{O}_{2}+2 \mathrm{NO} \rightarrow 2 \mathrm{NO}_{2} \\ &2 \mathrm{NO}_{2} \longrightarrow 2 \mathrm{NO}+2 \mathrm{O} \\ &2 \mathrm{O}+2 \mathrm{O}_{2} \longrightarrow 2 \mathrm{O}_{3} \longrightarrow \end{aligned} $$

Short answer

The catalyst is nitrogen monoxide (NO).

Step-by-step solution

Identify the Role of Each Compound

Review the reaction sequence to determine the role that nitrogen monoxide (\( \text{NO} \)) and nitrogen dioxide (\( \text{NO}_2 \)) play in the process. Start by examining where each compound appears in the sequence.

Analyze Nitrogen Monoxide (NO)

The first step of the sequence involves \( \text{NO} \) reacting with oxygen \((\text{O}_2)\) to form \( \text{NO}_2 \). In the second step, \( \text{NO}_2 \) decomposes back into \( \text{NO} \) and oxygen \((\text{O})\). This indicates that \( \text{NO} \) is regenerated.

Analyze Nitrogen Dioxide (NO₂)

In the second step, \( \text{NO}_2 \) is formed but then decomposes back to \( \text{NO} \) and \( \text{O} \) without being regenerated by the end of the full sequence, indicating it's not the compound that facilitates the reaction in a cyclic manner.

Identify the Catalyst

A catalyst is identified as a substance that participates in a reaction sequence and is regenerated by the end of the process. Since \( \text{NO} \) is consumed in the first step but fully regenerated in the second, it acts as a catalyst.

Key concepts

Ozone Formation

Ozone formation is a critical process in the Earth's atmosphere. Ozone, or O extsubscript{3}, forms in the stratosphere and helps protect the planet from harmful solar radiation. The process begins with molecular oxygen (O extsubscript{2}), a common diatomic molecule.

• Two O extsubscript{2} molecules can react under specific conditions to form ozone.
• This transformation contributes to the ozone layer's protective role.

Understanding the details of this formation helps in appreciating how human activities can impact atmospheric chemistry and, ultimately, climate and health.

Catalyst Identification

Identifying a catalyst involves examining the reaction sequence to see which substance mediates the reaction without being consumed.

• A catalyst accelerates a reaction and is regenerated by the end of the process.
• In the given reaction sequence, nitrogen monoxide (NO) interacts with molecular oxygen and is restored after the reaction.

This regeneration is key in identifying NO as the catalyst. NO remains unchanged but essential in facilitating both the continued conversion of O extsubscript{2} to O extsubscript{3} and maintaining the cycle.

Nitrogen Compounds

In ozone formation via catalytic reactions, nitrogen compounds like nitric oxide (NO) and nitrogen dioxide (NO extsubscript{2}) play crucial roles.

• NO acts as a catalyst, aiding in the conversion process.
• NO extsubscript{2} serves as an intermediary but doesn't complete the catalytic cycle.

These compounds are vital because they aid in breaking and reforming bonds within oxygen molecules, leading to the formation of ozone. This highlights the dynamic roles of nitrogen compounds in atmospheric chemistry.

Reaction Sequence

The reaction sequence is a series of chemical reactions where reactants transform into products through various steps.

• The sequence begins with O extsubscript{2} reacting with NO to form NO extsubscript{2}.
• Subsequently, NO extsubscript{2} decomposes back to NO and oxygen (O), which then forms ozone.

This systematic flow ensures the conservation of energy and matter. By understanding steps in detail, we can comprehend how each part connects to create a continuous cycle of ozone generation.

Chemical Regeneration

Chemical regeneration is a process where a chemical species returns to its original form after participating in a series of reactions.

• In the provided reactions, NO is regenerated, maintaining its catalytic role.
• This regeneration enables the reaction cycle to continue without additional input of NO.

Such regeneration is what allows NO to facilitate repeated ozone formation, showcasing its efficiency in catalytic reactions. This efficiency is vital in numerous industrial and environmental systems.