GCSE Chemistry (AQA)

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Calculating Theoretical Masses

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Quantitative chemistry Yield and atom economy of chemical reactions

Calculating Theoretical Masses

7:45 Percentage Yield
Spec 4.3.3.1
Previous Atom Economy Next Reaction Pathways
  • Percentage yield is calculated from actual and theoretical mass of the product.
  • Percentage yield indicates how well a reaction creates a product.
  • Equation: Percentage yield = (mass of product actually made / maximum theoretical mass of product) x 100.
  • Theoretical mass is the expected product if all reactants are used as expected.
  • Actual mass is usually lower due to side reactions, reactant loss, and incomplete reactions.
  • Actual mass of product can be measured by weighing solid products or measuring liquid volume.
  • Maximum theoretical mass can be calculated using the mass of reactant and balanced equation.
  • Example: Thermal decomposition of calcium carbonate to form calcium oxide and carbon dioxide.
  • Convert reactant mass to moles using the equation N = M / MR.
  • Use balanced equation to find moles of product.
  • Convert moles back to mass to find theoretical mass.
  • Example calculation: 20 grams of hydrogen gas burned with oxygen to produce water.
  • Balanced equation: 2 H2 + O2 ��� 2 H2O.
  • Calculate moles of hydrogen used and use balanced equation to find moles of water.
  • Convert moles of water to grams to find theoretical mass.
  • Calculate percentage yield using actual and theoretical mass.
  • Example result: Reaction has an 80% yield.

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