Understanding the Reaction

The decomposition of water (H₂O) into hydrogen (H₂) and oxygen (O₂) is represented by the following balanced chemical equation:

2H₂O → 2H₂ + O₂

Key Principle: The Law of Conservation of Mass

The Law of Conservation of Mass states that in a closed system, the total mass of the reactants before a chemical reaction must equal the total mass of the products after the reaction.

Calculation

1. Molar Mass of Water (H₂O): 18 g/mol (2 g/mol for H + 16 g/mol for O)

2. Moles of Water: 10 g / 18 g/mol = 0.556 moles H₂O

3. Moles of Hydrogen (H₂): From the balanced equation, 2 moles of H₂O produce 2 moles of H₂. So, 0.556 moles H₂O will produce 0.556 moles H₂.

4. Moles of Oxygen (O₂): From the balanced equation, 2 moles of H₂O produce 1 mole of O₂. So, 0.556 moles H₂O will produce 0.278 moles O₂.

5. Mass of Hydrogen (H₂): 0.556 moles H₂ * 2 g/mol = 1.112 g H₂

6. Mass of Oxygen (O₂): 0.278 moles O₂ * 32 g/mol = 8.90 g O₂

Total Mass of Products: 1.112 g H₂ + 8.90 g O₂ = 10.012 g

Conclusion

The total mass of the products (hydrogen and oxygen) from the decomposition of 10 grams of water is approximately 10 grams. This result aligns with the Law of Conservation of Mass.