Question

When hydrogen is burned in oxygen to form water, the composition of water formed does not depend on the amount of oxygen reacted. Interpret this in terms of the law of definite proportion.

Short answer

The composition of water formed from the reaction of hydrogen and oxygen does not depend on the amount of oxygen reacted, which adheres to the law of definite proportions. This law states that a chemical compound always contains its component elements in a fixed ratio by mass. In this case, the balanced chemical equation (2H2 + O2 → 2H2O) shows a 2:1 ratio of hydrogen to oxygen in water by molecule, and a 1:1 ratio by mass, confirming that water has a fixed composition according to the law of definite proportions.

Step-by-step solution

Identify the elements involved in the reaction.

In the given reaction, hydrogen (H) is burned in oxygen (O) to form water (H2O).

Write down the balanced chemical equation for the reaction.

To balance the chemical equation, we must ensure that the same number of each type of atom is present on both sides of the equation. The balanced chemical equation for the reaction is: \[2H_2 + O_2 \rightarrow 2H_2O\]

Observe the ratio of elements in the balanced equation.

In the balanced chemical equation, we see that two molecules of hydrogen react with one molecule of oxygen to form two molecules of water. Thus, the ratio of hydrogen to oxygen in the water is always 2:1 by molecule. This means there are two hydrogen atoms for every oxygen atom in a water molecule.

Interpret the given information in terms of the law of definite proportions.

The fact that the composition of water does not change, regardless of the amount of oxygen reacted, adheres to the law of definite proportions. No matter how much oxygen we use in the reaction, the ratio of hydrogen to oxygen in the resulting water will always be 2:1 by molecule (or 1:1 by mass, since hydrogen has approximately half the atomic mass of oxygen). This shows that water is a chemical compound with a fixed composition by mass, confirming the law of definite proportions.