Final answer:
In the reaction between octane and oxygen, with 0.280 mol of octane and 0.780 mol of oxygen, oxygen is the limiting reactant as only 0.780 mol O₂ is available while 3.5 mol is required to react with all the octane.
Step-by-step explanation:
To determine the limiting reactant in the reaction between octane and oxygen, we need to consider the balanced chemical equation for the combustion of octane (C₈H₁₈):
2 C₈H₁₈ (l) + 25 O₂ (g) → 16 CO₂ (g) + 18 H₂O (g)
Next, we calculate the mole ratio of the reactants based on the balanced equation. According to the stoichiometry of the reaction, 1 mole of octane reacts with 12.5 moles of oxygen. We have 0.280 moles of octane and 0.780 moles of oxygen.
For octane: 0.280 mol octane × (12.5 mol O₂ / 1 mol octane) = 3.5 mol O₂ required
Since only 0.780 mol of oxygen is available and we need 3.5 mol for the reaction to fully proceed with 0.280 mol of octane, oxygen is the limiting reactant. Octane is in excess because there is not enough oxygen to completely react with all of the octane available.