In a reaction with stoichiometry A + 2B → products, if you have 1 mole of A and 1 mole of B, which reactant is limiting?

In a reaction with stoichiometry A + 2B → products, if you have 1 mole of A and 1 mole of B, which reactant is limiting?

• A. A
• B. B
• C. Neither
• D. Both

Answer: (B)

The limiting reagent is found by comparing what you have to what the balanced equation requires. Here, one mole of the first reactant needs two moles of the second reactant for complete consumption of the first. With 1 mole of the first and 1 mole of the second, you can only use 1 mole of the second to react with 0.5 mole of the first, so the second reactant runs out first. That makes the second reactant the limiting one, and the first reactant remains in excess (about 0.5 mole left unreacted).

The limiting reagent is found by comparing what you have to what the balanced equation requires. Here, one mole of the first reactant needs two moles of the second reactant for complete consumption of the first. With 1 mole of the first and 1 mole of the second, you can only use 1 mole of the second to react with 0.5 mole of the first, so the second reactant runs out first. That makes the second reactant the limiting one, and the first reactant remains in excess (about 0.5 mole left unreacted).