Combustion stoichiometry for water formation: If 1 kg of hydrogen burns completely with 8 kg of oxygen, what total mass of liquid water is produced?

Introduction / Context:
This problem checks your understanding of basic combustion stoichiometry and conservation of mass. When hydrogen reacts with oxygen to form water, the chemical equation and molar masses determine the exact product mass, which is crucial in boiler calculations, fuel–air ratios, and emissions estimates.

Given Data / Assumptions:

• Chemical reaction: 2H2 + O2 → 2H2O (complete combustion, no side products).
• Masses given: 1 kg of hydrogen reacts with 8 kg of oxygen.
• Assume ideal, complete conversion to liquid water with no losses.

Concept / Approach:
The law of conservation of mass states that total mass of reactants equals total mass of products. The balanced equation shows a 1:1 mole ratio between H2 and H2O, but masses differ because molecular weights differ. Here, however, the problem already supplies the exact reacting masses, allowing a simple mass balance without converting to moles (though both routes agree).

Step-by-Step Solution:

Verification / Alternative check:
The molar method confirms the mass-balance method. Both demonstrate that all hydrogen and oxygen supplied in the given ratio end up in the water product, with no unreacted species for the ideal case.

Why Other Options Are Wrong:

• 1 kg of water: Ignores oxygen's mass contribution.
• 7 kg or 8 kg of water: Do not match total reactant mass; violate mass conservation.

Common Pitfalls:
Confusing mole and mass ratios, or forgetting to include oxygen's mass in the final product. Also, do not subtract; in combustion of elements, product mass equals the sum of reactant masses.

Final Answer:
9 kg of water