Limiting reagent
2 g of H2 reacts with 32 g of O2: 2H2 + O2 → 2H2O. What mass of water forms at most?
Answer B: explanation for every choice
A
This halves the correct result.
B
Correct. 1 mol H2 needs only 0.5 mol O2, so H2 is limiting and forms 1 mol (18 g) of water.
C
This adds the reactant masses, including oxygen that doesn't react.
D
This assumes O2 is limiting. 1 mol O2 would need 2 mol H2.
TakeawayFind the limiting reagent by comparing mole ratios, not masses.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID cp101.