Problem 127 - Introductory Chemistry Atoms First

Question

Hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\) can be made to decompose into water and oxygen as shown below. (The hydrogen peroxide in the beaker is decomposing to give a cloud of water vapor. Oxygen gas is also being produced.) Is this a redox reaction? If so, prove it.

Step-by-Step Solution

Answer

The decomposition of hydrogen peroxide (\(\mathrm{H}_{2}\mathrm{O}_{2}\)) is a redox reaction. The balanced chemical equation is \(2 \mathrm{H}_{2}\mathrm{O}_{2}(l) \rightarrow 2 \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{O}_{2}(g)\). The oxidation state of oxygen changes from -1 in \(\mathrm{H}_{2}\mathrm{O}_{2}\) to -2 in \(\mathrm{H}_{2}\mathrm{O}\) and 0 in \(\mathrm{O}_{2}\), indicating that the oxygen is being both reduced and oxidized during the reaction.

Step 1: Write down the given information

We are given the decomposition process of hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\), and our goal is to find out if this is a redox reaction or not.

Step 2: Write the balanced chemical equation for the decomposition of hydrogen peroxide

The balanced chemical equation for the decomposition of hydrogen peroxide is: \( 2 \mathrm{H}_{2}\mathrm{O}_{2}(l) \rightarrow 2 \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{O}_{2}(g) \) Here, 2 molecules of hydrogen peroxide decompose to form 2 molecules of water and 1 molecule of oxygen gas.

Step 3: Analyze the oxidation state of the elements

In order to determine if this reaction is a redox reaction, we need to find the oxidation state of the elements involved in the reaction: Oxidation state of: - Hydrogen in \(\mathrm{H}_{2}\mathrm{O}_{2}\): +1 - Oxygen in \(\mathrm{H}_{2}\mathrm{O}_{2}\): -1 - Hydrogen in \(\mathrm{H}_{2}\mathrm{O}\): +1 - Oxygen in \(\mathrm{H}_{2}\mathrm{O}\): -2 - Oxygen in \(\mathrm{O}_{2}\): 0

Step 4: Compare the oxidation states and determine if the reaction is redox

Comparing the oxidation states, we observe that the oxidation state of oxygen changed from -1 in \(\mathrm{H}_{2}\mathrm{O}_{2}\) to -2 in \(\mathrm{H}_{2}\mathrm{O}\) and 0 in \(\mathrm{O}_{2}\). Since there is a change in the oxidation state of the elements involved in the reaction, we can conclude that this is a redox reaction. The oxygen in hydrogen peroxide is being reduced to form water and oxidized to form oxygen gas.

Key Concepts

Decomposition Reaction

A decomposition reaction occurs when a single compound breaks down into two or more simpler substances. In the case of hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\), it decomposes into water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) and oxygen gas \(\left(\mathrm{O}_{2}\right)\). This type of reaction is generally represented by the equation \(AB \rightarrow A + B\), indicating that compound \(AB\) is breaking down into components \(A\) and \(B\).
For the decomposition of hydrogen peroxide, the equation is:

• \(2 \mathrm{H}_{2}\mathrm{O}_{2}(l) \rightarrow 2 \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{O}_{2}(g)\)

This reaction not only shows the breakdown of hydrogen peroxide into water and oxygen but also releases gases in the form of visible vapors.
Decomposition reactions, like this one, can happen under various conditions such as heating, light, or catalyst presence.
In industrial and laboratory settings, catalysts are often used to increase the rate of decomposition, making it an essential process in numerous applications.

Oxidation States

Understanding oxidation states is crucial to identifying redox reactions. The oxidation state of an element indicates the degree of oxidation an atom possesses in a molecule. It is helpful in determining how electrons are distributed within compounds. When examining a redox reaction, changes in oxidation states help us identify which elements are oxidized and which are reduced.
In hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\), the oxidation state of hydrogen is +1, and oxygen in this compound has an unusual oxidation state of -1. When it decomposes:

• In \(\mathrm{H}_{2}\mathrm{O}\), the oxidation state of hydrogen remains +1, but the oxidation state of oxygen changes to -2.
• In \(\mathrm{O}_{2}\), oxygen is in its elemental form with an oxidation state of 0.

These changes clearly demonstrate that hydrogen peroxide undergoes a redox reaction.
Oxygen is reduced (change from -1 to -2 as it forms water) and also oxidized (change from -1 to 0 as it forms oxygen gas).
This double behavior is a classic marker of redox reactions.

Hydrogen Peroxide

Hydrogen peroxide \((\mathrm{H}_{2} \mathrm{O}_{2})\) is a commonly used chemical compound known for its ability to act both as an oxidizing and reducing agent. This dual capability makes it useful in a wide range of applications.
It is a pale blue liquid in its pure form and is slightly more viscous than water. Its most common household use is as a disinfectant or bleaching agent. Due to its unstable molecular structure, it easily decomposes into water and oxygen, particularly when exposed to heat or light.
When viewing its decomposition as a redox reaction, hydrogen peroxide serves as a fascinating example of how substances can simultaneously undergo reduction and oxidation. This reactivity is harnessed not only in household cleaning products but also in industrial and environmental applications, such as wastewater treatment and rocket propulsion.

• Hydrogen peroxide acts as a disinfectant in medical settings due to its antibacterial properties.
• In hair dyes and cleaning agents, it plays a role in bleach formulations.
• In environmental science, it is used to remove pollutants.

These versatile uses highlight its importance across various fields, showcasing its practical relevance beyond simple chemical reactions.