Key Concepts in Reaction Yields

Reaction Yields

• Magnesium and hydrochloric acid produce hydrogen gas.
• Focus: limiting reactants, theoretical yield, percent yield.

Limiting and Excess Reactants

• Limiting Reactant: Reactant that is fully consumed; determines product amount.
• Excess Reactant: Not completely consumed; present after the reaction.

Identifying Limiting Reactants

• Calculate product yield from each reactant. The one yielding less is limiting.
• Divide moles of reactants by coefficients; the smallest quotient indicates the limiting reactant.

Theoretical and Actual Yield

• Theoretical Yield: Maximum product obtainable based on reactants.
• Actual Yield: Amount measured in lab; usually less than theoretical yield due to losses or side reactions.
• Percent Yield: Ratio of actual yield to theoretical yield, expressed as a percentage.

Example Reactions

• CH3OH and O2 Reaction:
     - Balanced Equation: 2 CH3OH + 3 O2 → 2 CO2 + 4 H2O
     - Limiting Reactant: O2
     - Moles after reaction: CH3OH = 1.167 mol, O2 = 0, CO2 = 0.333 mol, H2O = 0.667 mol.
  
• PCl5 and H2O Reaction:
     - Balanced Equation: PCl5 + 4 H2O → H3PO4 + 5 HCl
     - Limiting Reactant: PCl5, Yield = 0.250 mol H3PO4.

Mass Calculations

• Example: 0.40 g Al with 0.60 g Cl2 results in limiting Cl2; max AlCl3 produced = 1.50 g.

Common Yield Calculations

• Percent Yield Example: 0.450 mol Cl2 with 0.385 mol NaCl; calculate percent yield as per yield formula.