Problem 113 - Chemistry The Science in Context

Question

Is NO a catalyst for the decomposition of \(\mathrm{N}_{2} \mathrm{O}\) in the following two-step reaction mechanism, or is \(\mathrm{N}_{2} \mathrm{O}\) a catalyst for the conversion of \(\mathrm{NO}\) to \(\mathrm{NO}_{2} ?\) $$\text { (1) } \quad \mathrm{NO}(g)+\mathrm{N}_{2} \mathrm{O}(g) \rightarrow \mathrm{N}_{2}(g)+\mathrm{NO}_{2}(g)$$ $$\text { (2) } \quad 2 \mathrm{NO}_{2}(g) \rightarrow 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g)$$

Step-by-Step Solution

Answer

Answer: NO is a catalyst for the decomposition of N2O.

Step 1: Write down the given reactions

Let's list the given reactions: Reaction (1): $$\mathrm{NO}(g)+\mathrm{N}_{2} \mathrm{O}(g) \rightarrow \mathrm{N}_{2}(g)+\mathrm{NO}_{2}(g)$$ Reaction (2): $$2 \mathrm{NO}_{2}(g) \rightarrow 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g)$$

Step 2: Add the reactions to get the overall reaction

Add the reactions (1) and (2) to obtain the overall reaction: $$(\mathrm{NO}(g)+\mathrm{N}_{2} \mathrm{O}(g) \rightarrow \mathrm{N}_{2}(g)+\mathrm{NO}_{2}(g)) +(2 \mathrm{NO}_{2}(g) \rightarrow 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g))$$

Step 3: Simplify the overall reaction

Now, simplify the overall reaction by eliminating common intermediary species on both sides. In this case, we can eliminate the 2 NO and 2 NO2: $$\mathrm{N}_{2} \mathrm{O}(g) \rightarrow \mathrm{N}_{2}(g) + \mathrm{O}_{2}(g)$$

Step 4: Identify the catalyst

A catalyst is a substance that speeds up a reaction but is not consumed in the reaction and regenerated at the end. From the overall reaction, we can see that N2O decomposes into N2 and O2, so it is not a catalyst. On the other hand, NO is generated in reaction (1) and consumed in reaction (2) without being consumed in the overall reaction. This means that NO is the catalyst for the decomposition of N2O. So, the answer is: NO is a catalyst for the decomposition of N2O.

Key Concepts

Reaction Mechanism

In chemistry, a reaction mechanism is the detailed step-by-step description of how a chemical reaction occurs. This involves listing all the individual steps and identifying the various intermediates and products that form during the process. Understanding the reaction mechanism is essential for predicting the behavior and outcomes of a chemical reaction.

In the case of the decomposition of \(\mathrm{N}_2\mathrm{O}\), the reaction mechanism consists of two steps: first, \(\mathrm{NO}(g) + \mathrm{N}_2\mathrm{O}(g) \rightarrow \mathrm{N}_2(g) + \mathrm{NO}_2(g)\) and second, \(2\mathrm{NO}_2(g) \rightarrow 2\mathrm{NO}(g) + \mathrm{O}_2(g)\).

• The first step involves the reaction of \(\mathrm{NO}\) and \(\mathrm{N}_2\mathrm{O}\), leading to the formation of \(\mathrm{N}_2\) and \(\mathrm{NO}_2\).
• The second step is the conversion of \(\mathrm{NO}_2\) back to \(\mathrm{NO}\) and \(\mathrm{O}_2\).

By analyzing each step, we can determine the role of each reactant and identify which substances act as intermediates or catalysts. This understanding helps us in modifying reaction conditions to control the rate or selectivity of a desired reaction.

Overall Reaction

The overall reaction gives us the net change that happens between the reactants and products, without showing the detailed steps. It is derived by adding together all the individual reaction steps and simplifying by eliminating any intermediates that appear on both sides of the equation.

From the provided mechanism for the decomposition of \(\mathrm{N}_2\mathrm{O}\), we can deduce the overall reaction:

• Combine Step 1: \(\mathrm{NO}(g) + \mathrm{N}_2\mathrm{O}(g) \rightarrow \mathrm{N}_2(g) + \mathrm{NO}_2(g)\)
• With Step 2: \(2\mathrm{NO}_2(g) \rightarrow 2\mathrm{NO}(g) + \mathrm{O}_2(g)\)

This results in the overall balanced equation: \(\mathrm{N}_2\mathrm{O}(g) \rightarrow \mathrm{N}_2(g) + \mathrm{O}_2(g)\).

In this simplification, intermediates like \(\mathrm{NO}\) and \(\mathrm{NO}_2\) cancel out, revealing the actual transformation occurring, where \(\mathrm{N}_2\mathrm{O}\) decomposes to \(\mathrm{N}_2\) and \(\mathrm{O}_2\). Understanding the overall reaction is critical, as it tells us the net effect of an interaction, stripped of its complex steps, focusing on the conversion from initial to final states.

Decomposition

Decomposition reactions are a type of chemical reaction where a single compound breaks down into two or more simpler substances. It often requires an external energy source, such as heat, light, or electricity, to occur.

In this specific exercise, we investigate the decomposition of \(\mathrm{N}_2\mathrm{O}\), also known as nitrous oxide. It is a common example where the molecule breaks apart into \(\mathrm{N}_2\) (nitrogen gas) and \(\mathrm{O}_2\) (oxygen gas). In the presence of a catalyst, this reaction can occur more efficiently, which is where \(\mathrm{NO}\) comes into play as the catalyst.

• The breakdown involves the overall conversion: \(\mathrm{N}_2\mathrm{O}(g) \rightarrow \mathrm{N}_2(g) + \mathrm{O}_2(g)\).
• Decomposition reactions are significant in both natural processes and industrial applications.

Studying decomposition reactions is important for understanding how complex compounds can be broken down, which has implications in fields like environmental science, materials processing, and even understanding biochemical pathways. By leveraging catalysts, we can enhance these reactions, making them faster or requiring less input energy.