Video Transcript
During the formation of
photochemical smog, nitrogen dioxide can absorb light and undergo the following
reaction: NO2 reacts to produce NO plus O. Is nitrogen oxidized or reduced
during this reaction?
In this question, we need to
determine if nitrogen is oxidized or reduced during a decomposition reaction
process. We first need to explain the
reduction and oxidation processes. Then we can explain how these terms
relate to oxidation numbers. We can then determine the oxidation
number of nitrogen during the decomposition reaction. We can use all of this information
to determine the oxidation state of nitrogen before and after the decomposition
reaction process. We can then finally figure out the
answer to this question.
Chemists define reduction as a
chemical reaction process where a chemical species effectively gains electrons. They describe oxidation as a
chemical reaction process where a chemical species effectively loses electrons. Oxidation numbers explain the
oxidation or reduction state of an element. We can use oxidation numbers to
understand how a chemical species essentially gains or loses electrons during a
chemical reaction process.
Elements tend to have an increase
in oxidation number if they get oxidized during a chemical reaction. They have a decrease in oxidation
number if they get reduced during a chemical reaction process. Chemists state that a decrease in
oxidation number is indicative of a reduction process.
We have a general rule for
assigning an oxidation number to an atom of a two-element covalent system. We tend to give a negative
oxidation number to the element with the higher electronegativity number. We assign a positive oxidation
number to the chemical element with the lower electronegativity number.
Let us now compare the
electronegativity values of nitrogen and oxygen atoms in the NO2 and NO
molecules. Oxygen has a higher
electronegativity number than nitrogen. So oxygen will have a lower
oxidation number in the NO2 and NO molecules. Since oxygen is in group 16, group
16 elements tend to have an oxidation number of minus two. Nitrogen must therefore have the
oxidation number of plus four in NO2 and plus two in NO, since oxidation numbers
must have a sum of zero for a neutral molecule.
We see that the nitrogen gets a
lower oxidation number during the decomposition reaction process. We can see that the oxidation
number of nitrogen decreases from plus four to plus two as nitrogen dioxide forms
nitrogen monoxide. We can use this information to
figure out that nitrogen gets reduced during this decomposition reaction
process. We can end this video as we show it
has the answer “reduced.”
