Problem 94 - Chemistry

Question

What is the change in oxidation number for the following reaction? $$3 \mathrm{O}_{2} \longrightarrow 2 \mathrm{O}_{3}$$

Step-by-Step Solution

Answer

The change in oxidation number for oxygen in the reaction from O2 to O3 is \(+2/3\).

Step 1: Assign Oxidation Numbers

The oxidation number of an element in its elemental state (not combined with any other elements) is always zero. So, in \(\mathrm{O}_{2}\), each oxygen atom has an oxidation number of zero. In \(\mathrm{O}_{3}\) (ozone), each oxygen atom has a fractional oxidation number of \(+2/3\). This is because the total of the oxidation states in neutral molecules is zero. Hence, three oxygen atoms in O3 need to share two 'electrons' making it an average of \(+2/3\) per atom.

Step 2: Calculate Change in Oxidation Numbers

The change in oxidation numbers can be calculated by subtracting the initial oxidation number from the final oxidation number. Thus, the change in the oxidation number for oxygen going from O2 to O3 is \(+2/3 - 0 = +2/3\).

Key Concepts

Oxidation States

Oxidation states help us to understand electron distribution in compounds. They assign a hypothetical charge to each element. Although oxidation states are not actual charges, they are very useful for tracking electron transfer in chemical reactions.

• In free elements (like \(O_2\)), atoms have an oxidation state of 0.
• Combined elements usually follow rules: hydrogen is typically +1, oxygen is usually -2, and so on.
• In neutral compounds, the sum of oxidation states must equal zero.

In reactions, changes in oxidation states indicate a transfer of electrons. This helps to identify oxidizing and reducing agents. Remember these basics to confidently determine how electrons move in reactions.

Ozone (O3)

Ozone, or \(O_3\), might seem tricky because it is more complex than diatomic oxygen. Ozone is a triatomic molecule, meaning it consists of three oxygen atoms. Despite having the same elements, \(O_3\) and \(O_2\) have very different properties.

• Ozone is an allotrope of oxygen, existing at the same time in the element's different forms, similar to graphite and diamond in carbon.
• In an ozone molecule, the oxidation number isn't straightforward. For ozone, each oxygen atom carries an average oxidation state of \(\frac{+2}{3}\).
• This peculiar average arises because, for neutrality, the sum of oxidation states in \(O_3\) equals zero. Therefore, the oxidation states must balance.

Understanding the concept of oxidation numbers in \(O_3\) helps clarify its reactivity and role in atmospheric chemistry.

Elemental State

The elemental state of an element refers to its natural form when it is not combined with any other element. Elements in their elemental states help to set a baseline for measuring changes, especially in chemical reactions.

• In this state, elements like oxygen (\(O_2\)) have an oxidation number of zero. This means electrons are shared equally between the atoms.
• This state can help you easily identify changes during chemical reactions when the element forms compounds.
• Understanding an element's properties in its elemental state is crucial because it reveals insights when analyzing reactions and balancing equations.

By maintaining a grasp of the elemental state, you can better approach complex reactions and deduce the pathways of electrons.