weirdfacts

Convert each reactant amount to moles and compare n/coefficient. The smallest value sets the maximum reaction extent. Use that limiting reactant to calculate theoretical product, not whichever reactant has the smallest mass.

Percentage yield = actual product/theoretical product × 100, using the same units. Loss during separation, incomplete conversion and competing reactions can lower isolated yield.

Atom economy asks what fraction of the stoichiometric reactant mass becomes the desired product. It is different from experimental yield. A high-yield reaction can still generate substantial by-products. Green-chemistry evaluations are useful internal-assessment context in this syllabus.

INTERACTIVE MODEL

Which reactant runs out?

Stoichiometric proportionsTheoreticalActualn(NH₃)max = 2 × min(n(N₂), n(H₂)/3)
Theoretical NH₃: 4.00 mol · Actual: 3.20 mol

Stoichiometric maximum for N₂ + 3H₂ → 2NH₃, assuming complete conversion of the limiting reactant. The real Haber process is reversible; equilibrium may limit conversion further. Quantities are in mol.

Percentage yield = actual / theoretical × 100%
Assumed knowledge

n = m/M; ratios from a balanced chemical equation.

Learning checkpoints & sourceYOUR SYLLABUS CHECKPOINT
  • Find the limiting reagent from stoichiometry.
  • Calculate theoretical and percentage yield.
  • Distinguish yield from atom economy.
QCAA Chemistry 2025 v1.3 · p. 42
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