In the reaction N2 + 3H2 gives 2NH3, if 1 mole of nitrogen is mixed with 2 moles of hydrogen, the limiting reactant is
Correct answer: C. hydrogen, because 3 moles would be needed to react with 1 mole of nitrogen
- A. nitrogen, because it has the larger molar mass
- B. neither, because both are used up exactly
- C. hydrogen, because 3 moles would be needed to react with 1 mole of nitrogen
- D. nitrogen, because fewer moles of it are present
Explanation
The equation demands three moles of hydrogen for every mole of nitrogen, so 1 mole of nitrogen would need 3 moles of hydrogen and only 2 are available. Hydrogen therefore runs out first and limits the yield to two thirds of a mole of ammonia. Choosing the reactant present in the smaller number of moles without checking the ratio is the standard mistake.
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About Limiting and Excess Reactants
Limiting and excess reactants are identified from the balanced chemical equation and the available amounts of each substance. The limiting reactant determines the maximum product formed, while the excess reactant remains after completion, so questions require mole ratios, theoretical yield and sometimes percentage yield calculations.
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