In aerospace manufacturing, a protective oxide layer forms when solid aluminum reacts with… — Armed Services Vocational Aptitude Battery (ASVAB)

In aerospace manufacturing, a protective oxide layer forms when solid aluminum reacts with atmospheric oxygen gas according to the unbalanced chemical equation:

\underline{\quad}\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

To satisfy the Law of Conservation of Mass, what coefficient must be placed in front of $\text{Al}$ to properly balance this chemical equation?

A
$2$
B
$1$
$4$ Answer
D
$6$

Answer

The coefficient required in front of

\text{Al}

4

In the chemical equation, the product side shows two formula units of aluminum oxide (

2\text{Al}_2\text{O}_3

). Multiplying the leading coefficient of

2

by the subscript of

2

for aluminum gives

2 \times 2 = 4

aluminum atoms in the products. Conserving matter requires exactly

4

aluminum atoms on the reactant side, producing the balanced equation

4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

Step-by-Step Solution

Count the total number of aluminum atoms on the product side of the equation.

The product side contains

2\text{Al}_2\text{O}_3

, which has

2 \times 2 = 4

aluminum atoms.

According to the Law of Conservation of Mass, the number of atoms of each element must remain constant throughout a chemical reaction.

Determine the coefficient needed for aluminum on the reactant side to balance the four product aluminum atoms.

Since aluminum appears as an individual atom

\text{Al}

, a coefficient of

4

provides

4 \times 1 = 4

aluminum atoms.

Assigning a coefficient of

4

balances the equation completely:

4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

, with 4 aluminum atoms and 6 oxygen atoms on each side.

Key Concept

Balancing chemical equations by applying the Law of Conservation of Mass to ensure equal numbers of each atomic species among reactants and products.

Estimated Time:1m 0s

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