Percent Yield and Boyle's Law: Two Core Chemistry Calculations
How percent yield and Boyle's Law calculations work, explained with real lab-style examples.
Percent yield measures how a real reaction compares to theory; Boyle's Law measures how a gas responds to a changing container — two very different chemistry questions, both answered by simple ratio-based formulas.
Percent yield: reality vs. theoretical maximum
Percent Yield = (Actual Yield / Theoretical Yield) × 100. A reaction predicted to produce 50g of product by stoichiometry, but that actually yields 45g in the lab: (45/50) × 100 = 90% yield. The missing 10% is typically lost to side reactions, incomplete conversion, or losses during purification and transfer — real reactions essentially never hit 100% in practice.
Boyle's Law: pressure and volume, inversely linked
P1V1 = P2V2, holding temperature and the amount of gas constant. A gas at 1 atm occupying 10 liters is compressed down to 5 liters — solving for the new pressure: P2 = (P1×V1)/V2 = (1×10)/5 = 2 atm. Halving the volume exactly doubled the pressure, which is the defining inverse relationship Boyle's Law describes.
Why Boyle's Law only holds at constant temperature
The moment temperature changes too, Boyle's Law alone isn't sufficient — that's when the full ideal gas law (PV = nRT) is needed instead, since temperature independently affects pressure and volume. Boyle's Law is really just a special case of the ideal gas law where temperature and moles of gas are both held fixed.
Why percent yield can occasionally exceed 100%
A percent yield reported above 100% almost always signals a measurement or purity problem — commonly, leftover solvent, unreacted starting material, or moisture still present in the "product" being weighed, inflating its measured mass above what pure product alone would weigh. It's a red flag to investigate, not a sign of an unusually efficient reaction.
Common mistakes to avoid
- Comparing percent yield values across fundamentally different reaction types, where "excellent" yield expectations vary widely by reaction complexity
- Forgetting that Boyle's Law requires the same gas sample (no gas added or removed) between the two states being compared
- Using inconsistent pressure or volume units between P1V1 and P2V2 without converting to a common unit first
Calculate your own reaction and gas scenarios with the percent yield calculator and Boyle's Law calculator.