gen-define-limiting-reagents-and-give-one-short-worked-example-12f1

Define limiting reagents and give one short worked example.

# Limiting Reagents **Definition:** A limiting reagent (or limiting reactant) is the reactant that is completely consumed first in a chemical reaction, thereby determining the maximum amount of product that can be formed. Once the limiting reagent is used up, the reaction stops, even if other reactants remain. ## Worked Example **Problem:** If 4.0 g of hydrogen (H₂) reacts with 32.0 g of oxygen (O₂) to form water, which is the limiting reagent? **Reaction:** 2H₂ + O₂ → 2H₂O **Solution:** 1. **Convert masses to moles:** - Moles of H₂ = 4.0 g ÷ 2.0 g/mol = 2.0 mol - Moles of O₂ = 32.0 g ÷ 32.0 g/mol = 1.0 mol 2. **Compare mole ratio to stoichiometric ratio:** - Required ratio: 2 mol H₂ : 1 mol O₂ - Actual ratio: 2.0 mol H₂ : 1.0 mol O₂ - This matches perfectly (2:1), so neither is in excess *Alternative check:* For 2.0 mol H₂, we need 1.0 mol O₂ (which we have exactly) 3. **Conclusion:** Neither reagent is limiting in this case; they're in perfect stoichiometric proportions. However, if we had only 0.8 mol O₂, then **O₂ would be the limiting reagent**.