Question

I am taking General Chemistry 1 and I am studying redox reactions. I was looking at the following combustion reaction:

4CH3+7O2O: 0 →4CO2O:−2+6H2OO:−2
Under the reaction, I am labeling how the oxidation numbers for each oxygen atom. I noticed how the oxidation state on the left hand side of the reaction for O changes from 0 to -2 on the right hand side, even though there are now two sets of oxygen atoms in two different molecules.

What would happen if—disregarding the fact that O always has an oxidation of -2—the first molecule on the right hand side happened to have an O atom with an oxidation number of -2, but the second molecule happened to have an O with an oxidation number of -1? Is a situation like this possible in any reaction, with an element different than O? If so, how could the general change in oxidation number be described from the left hand side to the right hand side of the reaction?

EDIT: I found a reaction that details what I'm confused about:
2N2O5N:+5;O:−2(g) →4NO2N:+4;O:−2(g)+O2O: 0(g)
Here, it is obvious that nitrogen is reduced from an oxidation number of +5 to an oxidation number of +4, but how would you describe how the oxidation number of oxygen changes? On one molecule, its oxidation number stays the same, but on another, the oxidation number has gone up—has O been oxidized, or has it not changed?

Answer 1

In redox reactions, the change in oxidation numbers of different atoms within molecules can occur simultaneously but may not be uniform across all atoms of the same element. While a specific atom in a molecule may change its oxidation state, other atoms of the same element within different molecules can retain their original oxidation state. This scenario can lead to varied changes in oxidation numbers within the same reaction.

Step-by-step explanation:

The concept of oxidation numbers in redox reactions involves assigning hypothetical charges to atoms within molecules to track electron transfers. In the given example of 2N2O5 → 4NO2 + O2, nitrogen undergoes a reduction from +5 to +4 oxidation state. Concerning oxygen, within the NO2 molecule, the oxygen atom maintains an oxidation state of -2, consistent with its usual state in most compounds. However, in the O2 molecule formed, oxygen retains an oxidation state of 0.

This situation highlights the complexity of redox reactions where different molecules exhibit varying oxidation states for the same element. In this instance, while nitrogen undergoes a clear reduction, oxygen doesn't undergo a uniform change in oxidation state across different molecules involved in the reaction. It's crucial to differentiate between oxidation state changes within individual molecules and the overall change in the entire reaction.

For an element other than oxygen, a similar scenario might arise. In a reaction, different molecules or species might contain atoms of the same element with distinct oxidation states. The net change in oxidation state across the entire reaction should be determined by considering the individual changes in oxidation numbers for each element in different molecules involved. This variability demonstrates the non-uniform nature of oxidation state changes within a single reaction, highlighting the importance of examining the oxidation states of each atom separately rather than assuming uniform changes across all instances of the same element.