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Difficulty: HardDefinitions and Classical vs Modern Concepts of Redox
Ammonia gas (NH3\text{NH}_3) reacts with oxygen gas (O2\text{O}_2) over a platinum-rhodium catalyst to form nitrogen(II) oxide (NO\text{NO}) and water vapor (H2O\text{H}_2\text{O}) according to the equation:
4NH3(g)+5O2(g)→4NO(g)+6H2O(g)4\text{NH}_{3(g)} + 5\text{O}_{2(g)} \rightarrow 4\text{NO}_{(g)} + 6\text{H}_2\text{O}_{(g)}

Which of the following statements correctly interprets the oxidation process occurring in this reaction from both classical and modern redox perspectives?

  1. Ammonia is oxidized because nitrogen loses hydrogen classically, which corresponds to an increase in the oxidation state of nitrogen from −3-3 to +2+2.Answer
  2. B
    Oxygen gas is reduced because elemental O2\text{O}_2 starts with an oxidation state of −2-2 and gains hydrogen to form H2O\text{H}_2\text{O}.
  3. C
    Ammonia acts as an oxidizing agent because nitrogen loses electrons, resulting in a decrease in its oxidation state.
  4. D
    Oxygen gas acts as a reducing agent because its oxidation number increases from −2-2 to 00 as it forms water.

Answer

Ammonia is oxidized because nitrogen loses hydrogen classically, which corresponds to an increase in the oxidation state of nitrogen from −3-3 to +2+2.
In classical terminology, oxidation involves the removal of hydrogen or addition of oxygen. Ammonia (NH3\text{NH}_3) loses hydrogen to form nitrogen(II) oxide (NO\text{NO}), fulfilling classical oxidation. In modern electronic terms, the oxidation number of nitrogen increases from −3-3 in NH3\text{NH}_3 to +2+2 in NO\text{NO}, representing a loss of 5 electrons per nitrogen atom, which directly aligns with the modern definition of oxidation.

Step-by-Step Solution

1
Analyze classical redox definitions for ammonia
In NH3\text{NH}_3, nitrogen is combined with hydrogen. In forming NO\text{NO}, hydrogen is removed and oxygen is added. Classically, loss of hydrogen and gain of oxygen both define oxidation.
Classical redox concepts define oxidation as the gain of oxygen or loss of hydrogen.
2
Determine oxidation states for nitrogen in reactants and products
In NH3\text{NH}_3, hydrogen is +1+1, so N+3(+1)=0⇒N=−3N + 3(+1) = 0 \Rightarrow N = -3. In NO\text{NO}, oxygen is −2-2, so N+(−2)=0⇒N=+2N + (-2) = 0 \Rightarrow N = +2.
Sum of oxidation numbers in a neutral molecule equals zero.
3
Correlate modern redox definition with classical observation
The change in oxidation state of nitrogen from −3-3 to +2+2 is an increase of 55, which corresponds to loss of electrons (oxidation).
Modern redox concepts define oxidation as an increase in oxidation state due to loss of electrons.

Key Concept

Integration of Classical (Hydrogen/Oxygen Transfer) and Modern (Oxidation Number/Electron Transfer) Redox Concepts
Estimated Time:2m 0s
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Topics

Definitions and Classical vs Modern Concepts of Redox

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