how many grams of hydrogen gas are needed to react with 688 grams of oxygen to make water? (3 sig figs)​

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