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Difficulty: MediumChemical Reactions and Compounds
In industrial metallurgy, solid aluminum metal reacts with oxygen gas at elevated temperatures to form solid aluminum oxide according to the unbalanced chemical equation:
\text{__}\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3
Determine the missing stoichiometric coefficient required to balance this chemical equation and complete the statement below.
Answer:To satisfy the law of conservation of mass, the stoichiometric coefficient placed before Al\text{Al} must be 【4】.

Answer

The stoichiometric coefficient for aluminum is 4.
The coefficient 4 correctly balances the equation because the product side has 2 formula units of Al2O3\text{Al}_2\text{O}_3, containing a total of 2×2=42 \times 2 = 4 aluminum atoms. In accordance with the law of conservation of mass, matter cannot be created or destroyed in a chemical reaction, requiring 4 aluminum atoms on the reactant side (4Al+3O2→2Al2O34\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3).

Step-by-Step Solution

1
Count the total number of aluminum and oxygen atoms present in the products.
The product side contains 2Al2O32\text{Al}_2\text{O}_3, which has 2×2=42 \times 2 = 4 aluminum atoms and 2×3=62 \times 3 = 6 oxygen atoms.
Coefficients multiply all subscripts within a chemical formula to give total atom counts.
2
Verify oxygen atom balance on the reactant side.
The reactant side has 3O23\text{O}_2, which equals 3×2=63 \times 2 = 6 oxygen atoms, perfectly matching the product side.
Verifying one element ensures that only the unknown coefficient needs adjustment.
3
Determine the coefficient for elemental aluminum on the reactant side.
Since single aluminum atoms are represented as Al\text{Al}, placing a coefficient of 4 yields 4×1=44 \times 1 = 4 aluminum atoms.
The law of conservation of mass requires the same number of each type of atom on both sides of the equation.

Key Concept

Balancing Chemical Equations via Mass Conservation
Estimated Time:1m 0s
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Topics

Chemical Reactions and Compounds

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