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Difficulty: MediumChemical Reactions and Compounds

When an iron nail is exposed to moist air over several weeks, it reacts with oxygen gas to form iron(III) oxide (rust), as represented by the balanced equation 4Fe+3O2→2Fe2O34\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3. Which of the following statements correctly explains why this process is classified as a chemical change?

  1. A
    The iron metal merely undergoes a state change from solid to liquid due to environmental humidity.
  2. B
    The iron nail dissolves reversibly in atmospheric water vapor without forming any new chemical bonds.
  3. New chemical bonds are formed between iron and oxygen atoms, producing a substance with different chemical properties.Answer
  4. D
    The chemical formula subscripts of the elemental reactants change during the reaction to force the equation to balance.

Answer

New chemical bonds are formed between iron and oxygen atoms, producing a substance with different chemical properties.
The reaction produces iron(III) oxide (Fe2O3\text{Fe}_2\text{O}_3), which is a distinct compound with chemical and physical properties entirely different from elemental iron and gaseous oxygen. Because chemical bonds are broken and new bonds are formed, the process is a chemical change.

Step-by-Step Solution

1
Analyze the reactants and products in the reaction 4Fe+3O2→2Fe2O34\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3.
Elemental iron (Fe\text{Fe}) and oxygen gas (O2\text{O}_2) react to produce the compound iron(III) oxide (Fe2O3\text{Fe}_2\text{O}_3).
Determining the chemical formulas reveals whether original substances underwent composition changes.
2
Distinguish between a physical change and a chemical change.
Physical changes alter appearance or physical state without changing chemical identity, whereas chemical changes form new chemical bonds and new substances.
Rust possesses distinct chemical reactivity, color, and magnetic properties compared to metallic iron and oxygen gas.
3
Identify the statement matching the definition of a chemical change.
The formation of new bonds producing a compound with distinct properties defines the reaction as a chemical change.
This directly demonstrates the fundamental principle of chemical reactions.

Key Concept

Chemical change versus physical change and compound formation
Estimated Time:1m 0s
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Topics

Chemical Reactions and Compounds

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