In the reaction 2 H_2 + O_2 → 2 H_2O, if you have 5.0 mol of H_2 and 2.0 mol of O_2, which reactant is the limiting reactant?

• A. H_2
• B. O_2
• C. Both are limiting
• D. Neither is limiting

Answer: (B)

Verified step by step guidance

1. Write down the balanced chemical equation: \$2\ H_2 + O_2 \rightarrow 2\ H_2O$.
2. Identify the mole ratio of the reactants from the balanced equation: 2 moles of \(H_2\) react with 1 mole of \(O_2\).
3. Calculate the amount of \(O_2\) needed to react completely with 5.0 moles of \(H_2\) using the mole ratio: \(\text{moles of } O_2 = \frac{5.0\ \text{mol } H_2}{2} = 2.5\ \text{mol } O_2\).
4. Compare the calculated required moles of \(O_2\) (2.5 mol) with the actual moles of \(O_2\) available (2.0 mol). Since 2.0 mol \(O_2\) is less than 2.5 mol required, \(O_2\) is the limiting reactant.
5. Confirm that \(H_2\) is in excess because there is more \(H_2\) than needed to react with the available \(O_2\).