In a reaction with stoichiometry A + 2B → products, if you start with 3 moles A and 3 moles B, which reagent is limiting?

In a reaction with stoichiometry A + 2B → products, if you start with 3 moles A and 3 moles B, which reagent is limiting?

• A. A
• B. Neither
• C. Both
• D. B

Answer: (D)

In this reaction, the limiting reagent is the one that runs out first given the stoichiometry. Here, every mole of A needs 2 moles of B. If you try to use up all the A, you’d need 6 moles of B, but you only have 3 moles of B. So B is consumed first, leaving A in excess. The reaction will stop when B is gone, making B the limiting reagent. The other options don’t fit because A isn’t limiting (there isn’t enough B to use up all of A), and there isn’t a scenario where neither or both reagents are limiting.

In this reaction, the limiting reagent is the one that runs out first given the stoichiometry. Here, every mole of A needs 2 moles of B. If you try to use up all the A, you’d need 6 moles of B, but you only have 3 moles of B. So B is consumed first, leaving A in excess. The reaction will stop when B is gone, making B the limiting reagent. The other options don’t fit because A isn’t limiting (there isn’t enough B to use up all of A), and there isn’t a scenario where neither or both reagents are limiting.