Question

Examine the unbalanced equation.

Answer 1

Answer:

The correct answer is:

4 Al + 3 O₂ → 2 Al₂O₃

Explanation:

The law of conservation of matter states that since no atom can be created or destroyed in a chemical reaction, the number of atoms that are present in the reagents has to be equal to the number of atoms present in the products.

Then, you must balance the chemical equation to comply with the previous law. For that, you must first look at the subscripts next to each atom to find the number of atoms in the equation. If the same atom appears in more than one molecule, you must add its amounts . In this case:

Left side: 2 aluminum and 2 oxygen.

Right side: 2 aluminum and 3 oxygen.

The coefficients located in front of each molecule indicate the amount of each molecule for the reaction. This coefficient can be modified to balance the equation, just as you should never alter the subscripts.

By multiplying the coefficient mentioned by the subscript, you get the amount of each element present in the reaction.  

First of all, it is convenient to start balancing the oxygen. In this case you can see that you have 2 on the left side and 3 on the right side. A simple way to balance the oxygen then is to exchange these numbers sideways, placing them as  coefficients in front of each molecule that corresponds. Then you get:

___Al + 3 O₂ → 2 Al₂O₃

Now you have:

Left side: 2 aluminum and 6 (3*2) oxygen.

Right side: 4 (2*2) aluminum and 6 (3*2) oxygen.

Now that the oxygen is balanced, you balance the aluminum as follows:

4 Al + 3 O₂ → 2 Al₂O₃

Now you have:

Left side: 4 aluminum and 6  oxygen.

Right side: 4 (2*2) aluminum and 6  oxygen.

Since you have the same amount of each element on each side of the equation, the equation is balanced.

So the correct answer is:

4 Al + 3 O₂ → 2 Al₂O₃

Answer 2

___Al + ___O2 → ___Al2O3

4Al + 3O2 → 2Al2O3