Problem 66 - Chemistry Principles and Practice

Question

Write two reactions that show how NO gas can catalytically decompose large amounts of ozone, \(\mathrm{O}_{3}\).

Step-by-Step Solution

Answer

NO catalytically decomposes ozone through the reactions: \(\mathrm{NO} + \mathrm{O}_3 \rightarrow \mathrm{NO}_2 + \mathrm{O}_2\) and \(\mathrm{NO}_2 + \mathrm{O}_3 \rightarrow \mathrm{NO} + 2\mathrm{O}_2\).

Step 1: Understanding the role of NO

Nitric oxide (NO) is a catalyst in ozone decomposition. Catalysts speed up chemical reactions without being consumed. We will write two reactions where NO helps in decomposing ozone but is regenerated at the end of the process.

Step 2: Write the first reaction

In the first reaction, ozone (\(\mathrm{O}_3\)) reacts with NO to form nitrogen dioxide (\(\mathrm{NO}_2\)) and oxygen (\(\mathrm{O}_2\)).\[\mathrm{NO} + \mathrm{O}_3 \rightarrow \mathrm{NO}_2 + \mathrm{O}_2\]

Step 3: Write the second reaction

In the second reaction, nitrogen dioxide (\(\mathrm{NO}_2\)) reacts with another ozone molecule (\(\mathrm{O}_3\)) to regenerate nitric oxide (NO) and form two molecules of oxygen (\(\mathrm{O}_2\)).\[\mathrm{NO}_2 + \mathrm{O}_3 \rightarrow \mathrm{NO} + 2\mathrm{O}_2\]

Step 4: Verify the catalytic cycle

NO is consumed in the first reaction but regenerated in the second reaction, confirming its role as a catalyst. Ozone (\(\mathrm{O}_3\)) is decomposed into oxygen (\(\mathrm{O}_2\)) through these reactions.

Key Concepts

Catalysis

Catalysis plays a vital role in speeding up chemical reactions, acting like a supercharger for the process. A catalyst is a substance that accelerates the reaction without being consumed in the process. It works by providing an alternative pathway for the reaction, which requires less energy. As a result, the rate of reaction increases.

In the context of ozone decomposition, nitric oxide (NO) acts as a catalyst. This means it aids the reaction whereby ozone (\(\mathrm{O}_3\)) is converted into oxygen (\(\mathrm{O}_2\)) repeatedly without actually being used up itself.

NO's behavior is typical for a catalyst. It enters the reaction, forms an intermediate compound, but is eventually regenerated. Therefore, it can continue to catalyze additional reactions, enhancing the efficiency of the ozone decomposition process.

Chemical Reactions

Chemical reactions involve the transformation of reactants into products. This involves breaking and making chemical bonds, which leads to the formation of new substances. The decomposition of ozone is a two-step chemical reaction facilitated by nitric oxide.

In the first reaction, \(\mathrm{NO}\) reacts with ozone (\(\mathrm{O}_3\)) to form nitrogen dioxide (\(\mathrm{NO}_2\)) and oxygen (\(\mathrm{O}_2\)). This step shows the chemical transformation where the catalyst first participates in forming new products.

In the subsequent reaction, nitrogen dioxide then reacts with another ozone molecule. The products of this reaction are \(\mathrm{NO}\), which is regenerated, and oxygen. This final step ensures that nitric oxide is not consumed permanently and illustrates the reversible nature of catalytic chemical reactions.

Let's not forget: for a successful reaction, the conditions such as temperature and pressure might need to be optimized to allow the process to proceed efficiently.

Nitric Oxide

Nitric oxide is a versatile molecule often found in a range of chemical and biological processes. In atmospheric chemistry, it plays a significant role due to its ability to facilitate catalytic reactions like the decomposition of ozone (\(\mathrm{O}_3\)).

The unique chemical properties of NO enable it to alternate between active and passive states in a reaction. This capability is what makes it an effective catalyst. In ozone decomposition, NO initially reacts with ozone to form nitrogen dioxide and oxygen. Importantly, in its subsequent reaction with another ozone molecule, NO is regenerated. This ensures that NO can continue its role, decomposing further ozone molecules.

Apart from its role in ozone decomposition, nitric oxide has various environmental and physiological impacts. It's involved in air quality dynamics and is a crucial signaling molecule in animal systems. Therefore, understanding its interaction with ozone is essential for environmental chemistry and ecological health.