Asked in ETEA MDCAT 2006 2006Moderate

If 28.0g nitrogen gas is reacted with 8.0g of hydrogen gas to form ammonia, the limiting reactant among the two will be:

Correct answer: A. N2

  • A. N2
  • B. H2
  • C. both (a) & (b)
  • D. None of these

Explanation

The balanced chemical equation for the production of ammonia is: N2 + 3H2 → 2NH3. From this equation, 1 mole of nitrogen reacts with 3 moles of hydrogen. Calculate the moles of each reactant: 28.0g of N2 is 1 mole (since the molar mass of N2 is 28.0 g/mol), and 8.0g of H2 is approximately 4 moles (since the molar mass of H2 is 2.0 g/mol). Given this, the reaction requires 3 moles of H2 for every mole of N2. Hence, the 4 moles of H2 are in excess, making N2 the limiting reactant. Option A is correct. Options B, C, and D are incorrect because hydrogen is in excess, and only one reactant can be the limiting reactant.

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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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