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Answer:
86 g H₂
Explanation:
The reaction between hydrogen gas (H₂) and oxygen gas (O₂) to produce water (H₂O) is described by the following balanced chemical equation:
2 H₂(g) + O₂(g) → 2 H₂O(g)
As we can see, 2 moles of H₂ reacts with 1 mol of O₂. We have to convert the moles to mass by using the molar mass (MM) of each compound:
MM(H₂) = 1 g/mol x 2 = 2 g/mol
2 moles H₂ = 2 mol x 2 g/mol = 4 g
MM(O₂) = 16 g/mol x 2 = 32 g/mol
1 mol O₂ = 1 mol x 32 g/mol = 32 g
Thus, 4 grams of H₂ reacts with 32 g of O₂. The stoichiometric ratio H₂/O₂ is 4 g H₂/32 g O₂. So, we multiply the stoichiometric ratio by the mass of O₂ we have (688 g) to calculate the grams of H₂ we need:
4 g H₂/32 g O₂ x 688 g O₂ = 86 g H₂