Problem 17 - Chemistry

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.

Step-by-Step Solution

Answer

The composition of water remains unchanged when hydrogen is burned in oxygen, regardless of the amount of oxygen reacted, due to the Law of Definite Proportions. This law states that elements in a compound always combine in a fixed mass ratio. For water, the mass ratio of hydrogen to oxygen is 2:1, and this ratio prevails no matter the amounts of hydrogen and oxygen participating in the reaction, upholding the consistent composition of water.

Step 1: Understand the chemical reaction

Initially, we need to have a grasp of the chemical reaction involved. In this process, hydrogen gas (H2) reacts with oxygen gas (O2) to form water (H2O). The balanced chemical equation for this reaction is: `\(2H_2 + O_2 \rightarrow 2H_2O\)`

Step 2: Law of Definite Proportions

According to the Law of Definite Proportions, the ratio of the reacting elements or compounds in a chemical reaction remains constant, regardless of their quantities. In other words, for a specific compound like water, the elements will combine in a fixed mass ratio. For the formation of water, this ratio is: `Hydrogen : Oxygen = 2:1` (by mass)

Step 3: Interpreting the reaction

Hydrogen and oxygen will react with each other in the fixed mass ratio stated above. If the amount of oxygen reacted changes, the amount of hydrogen that reacts will also change to maintain the 2:1 mass ratio. However, the composition of the water molecules formed remains unchanged. This is because, according to the Law of Definite Proportions, the fixed mass ratio of hydrogen and oxygen in water will always be the same, regardless of the quantities of the reacting elements.

Step 4: Conclusion

The fact that the composition of water formed does not depend on the amount of oxygen reacted can be interpreted as a demonstration of the Law of Definite Proportions, which states that elements in a compound will always combine in a constant mass ratio. In the case of water, this is a 2:1 mass ratio of hydrogen to oxygen, which means the composition of water will remain unchanged regardless of the amounts of hydrogen and oxygen involved in the reaction.