Final answer:
In the chemical reaction 2 H2 + O2 → 2 H2O, with 20.0 moles of O2 and 30.0 moles of H2, H2 is the limiting reactant because it will run out first, as there is enough O2 to react with 40 moles of H2.
Step-by-step explanation:
To determine the limiting reactant, we need to compare the mole ratios of the reactants given in the balanced chemical reaction with the amounts available. The reaction is as follows:
2 H₂(g) + O₂(g) → 2 H₂O(g)
This tells us that 2 moles of hydrogen gas (H₂) reacts with 1 mole of oxygen gas (O₂) to produce 2 moles of water (H₂O). Given the amounts of reactants, we have 20.0 moles of O₂ and 30.0 moles of H₂.
To find out which reactant will run out first, let's set up a ratio based on the stoichiometry of the balanced equation:
- For O₂: we have 20.0 moles available, and the reaction requires 1 mole of O₂ for every 2 moles of H₂. This means we have enough O₂ to react with 40.0 moles of H₂.
- For H₂: we have 30.0 moles available, and the reaction requires 2 moles of H₂ for every 1 mole of O₂. Therefore, we have enough H₂ to completely react with 15.0 moles of O₂.
Since we only have 20.0 moles of O₂ and we would need 40.0 moles of H₂ to fully react with it, and we have 30.0 moles of H₂, this means that hydrogen (H₂) is the molecule that will run out first, making it the limiting reactant. So, the correct answer is Option 2: H₂.