Problem 62 - Introductory Chemistry Atoms First

Question

In the upper atmosphere, sunlight can convert oxygen to ozone: \(2 \mathrm{O}_{2} \rightarrow \mathrm{O}_{3}+\mathrm{O}\) Ozone Is this a redox reaction? Completely justify your answer.

Step-by-Step Solution

Answer

No, this is not a redox reaction. The oxidation states of oxygen in the reactants (O₂) and the products (O₃ and O) are all 0, and no changes in oxidation states occur during this reaction.

Step 1: Identify the initial and final oxidation states of the elements involved

Start by identifying the initial and final oxidation states for oxygen in the reactants (O₂) and in the products (O₃ and O). The oxygen molecule (O₂) has an oxidation state of 0, since it is in its elemental form. For ozone (O₃), we will need to determine the oxidation states of the individual oxygen atoms. For atomic oxygen (O), the oxidation state is also 0, as it is the elemental form of oxygen.

Step 2: Determine the oxidation states of oxygen in ozone (O₃)

Let's assign oxidation state variable x to each oxygen atom in O₃, and set up the equation: 3x = 0 (since the overall charge of the O₃ molecule is 0) Solving this equation for x yields: x = 0 So, each oxygen atom in ozone (O₃) has an oxidation state of 0.

Step 3: Compare the initial and final oxidation states of the elements

Now that we have found the oxidation states of oxygen in the reactants and the products, we can compare them: Oxygen gas (O₂): Oxidation state 0 Ozone (O₃): Oxidation state 0 Atomic oxygen (O): Oxidation state 0

Step 4: Determine if the reaction is a redox reaction

A reaction is classified as a redox reaction if there is a change in the oxidation states of the elements involved. In this case, the oxidation states of oxygen in the reactants (O₂) and the products (O₃ and O) remain unchanged at 0. Therefore, this reaction is not a redox reaction.

Key Concepts

Oxidation State

The concept of oxidation state helps us understand the charge distribution in a molecule. It indicates the number of electrons that an atom gains, loses, or shares in a chemical bond.
The oxidation state is crucial for categorizing chemical reactions, especially redox reactions, where electrons are transferred between atoms.

• In elemental form, any element, like oxygen (O₂), has an oxidation state of 0.
• For compounds, oxidation states help assign charges to atoms assuming all electrons were shared equally between atoms.

Understanding oxidation states helps chemists determine if a redox reaction occurs by checking if oxidation states change during the reaction.

Ozone Formation

Ozone, a molecule composed of three oxygen atoms, can be created through the action of sunlight on oxygen (O₂). This process is crucial to our environment.

• In the upper atmosphere, high-energy ultraviolet (UV) light from the sun splits oxygen molecules into individual oxygen atoms.
• These free oxygen atoms can then collide with other oxygen molecules to form ozone (O₃).

Ozone plays a vital role in blocking harmful UV radiation from reaching the Earth's surface, thereby protecting living organisms.

Upper Atmosphere Chemical Reactions

Chemical reactions in the upper atmosphere are primarily driven by sunlight and involve gases like oxygen and ozone.
These reactions are essential for maintaining the Earth's energy balance and biological shielding.

• Sunlight breaks down molecular oxygen (O₂) into individual oxygen atoms.
• These oxygen atoms are highly reactive and partake in forming ozone and other molecules.

The continuous cycle of ozone formation and decomposition regulates the concentration of ozone in the atmosphere, maintaining a delicate balance to protect life on Earth.

Oxygen Molecules (O₂)

Oxygen molecules are made up of two oxygen atoms bonded together. They are abundant in the atmosphere and are essential for life.
In the upper atmosphere, they undergo various chemical reactions driven by sunlight.

• O₂ is stable and carries no overall charge, with both oxygen atoms having an oxidation state of 0.
• It participates in crucial atmospheric reactions, such as ozone formation.

Understanding oxygen's role in these reactions is critical for grasping how our atmosphere filters harmful solar radiation and sustains life.