Problem 118 - Chemistry: An Atoms-Focused Approach

Question

Explain why NO is a catalyst in the following two-step process that results in the depletion of ozone in the stratosphere: (1) \(\quad \mathrm{NO}(g)+\mathrm{O}_{3}(g) \rightarrow \mathrm{NO}_{2}(g)+\mathrm{O}(g)\) (2) \(\quad \mathrm{O}(g)+\mathrm{NO}_{2}(g) \rightarrow \mathrm{NO}(g)+\mathrm{O}_{2}(g)\) Overall: \(\quad \mathrm{O}(g)+\mathrm{O}_{3}(g) \rightarrow 2 \mathrm{O}_{2}(g)\)

Step-by-Step Solution

Answer

Answer: NO is considered a catalyst in the given two-step process of ozone depletion because it helps increase the rate of the reaction without being consumed. It participates in the reaction temporarily and is regenerated at the end of the process, making it a catalyst in the overall depletion of ozone in the stratosphere.

Step 1: Understand the reactions

In the given two-step process, the first reaction involves nitrogen monoxide (NO) reacting with ozone (O3) to form nitrogen dioxide (NO2) and an oxygen atom (O). In the second reaction, the oxygen atom reacts with NO2 to form NO and an oxygen molecule (O2).

Step 2: Identify the final product

Combining the two reactions, we get the overall reaction: O(g) + O3(g) → 2 O2(g) This reaction represents the depletion of ozone, where an oxygen atom and an ozone molecule combine to form two oxygen molecules.

Step 3: Determine the role of NO

Let's examine the change in NO throughout the reactions. In the first reaction, NO is consumed, while NO2 is produced. In the second reaction, NO is produced and NO2 is consumed. This means that, after both reactions occur, the initial amount of NO is regenerated. Consequently, NO does not undergo any net change and is not consumed in the overall reaction.

Step 4: Define a catalyst

A catalyst is a substance that increases the rate of a chemical reaction, without being consumed. It participates in the reaction temporarily, helping the molecules to react, but is regenerated at the end of the process.

Step 5: Conclude the role of NO

Since NO is not consumed in the two-step process and is regenerated at the end of the reaction, we can conclude that NO acts as a catalyst in this process that results in the depletion of ozone in the stratosphere.

Key Concepts

Catalyst

A catalyst is a fascinating component in chemistry. It speeds up chemical reactions without being consumed or permanently altered. How does it manage this? By providing an alternative reaction pathway with lower activation energy.
In other words, it helps the reactants interact more efficiently. Catalysts remain unchanged at the end of the reaction.
This makes them valuable in various processes as they can be used over and over again.

• Increases reaction rate
• Not consumed in the reaction
• Regenerated and unchanged

Catalysts are essential in environmental chemistry too. For instance, they play a crucial role in reducing ozone depletion in the stratosphere.

Nitrogen Monoxide (NO)

Nitrogen Monoxide, also known as nitric oxide, is a simple yet crucial molecule in atmospheric chemistry. It has various roles but is particularly notable when discussing air pollution and ozone chemistry.
In the context of ozone depletion, NO acts as a catalyst. It participates in reactions without being consumed, facilitating the breakdown of ozone molecules.

• Acts as a catalyst in ozone-depleting reactions
• Regenerates itself after reactions
• Contributes to pollution but also aids studies in atmospheric chemistry

Understanding NO's role is critical to grasping the mechanisms behind ozone layer depletion.

Stratosphere

The stratosphere is a layer of Earth's atmosphere situated above the troposphere, typically spanning heights from 10 km to 50 km. This region plays a critical role in life on Earth as it contains the ozone layer.
The ozone layer absorbs and scatters ultraviolet solar radiation. This shields living organisms on Earth from harmful UV rays. However, certain chemical reactions, like those involving nitrogen monoxide, can deplete ozone levels.

• Second layer of Earth's atmosphere
• Home to the protective ozone layer
• Site of critical atmospheric reactions

Understanding the stratosphere is crucial for comprehending where and how ozone depletion occurs.

Chemical Reaction Mechanism

A chemical reaction mechanism details each step of a chemical process, illustrating how reactants transform into products. This concept is vital for understanding complex reactions like the two-step process involving nitrogen monoxide and ozone.
In the provided mechanism:

• First, NO reacts with ozone to form NO2 and a free oxygen atom.
• Then, this oxygen atom reacts with NO2 to regenerate NO and produce O2.

The beauty of the mechanism lies in its ability to reveal why NO serves as a catalyst, showing how it enters and exits the reactions unchanged. By focusing on individual steps, scientists can manipulate conditions to enhance desired reactions or inhibit harmful ones.