Reaction Yields

Percentage Yield

• In a lot of reactions, not all reactants react to form products which can be due to several factors:

  • Other reactions take place simultaneously

  • The reaction does not go to completion

  • Reactants or products are lost to the atmosphere

• The percentage yield shows how much of a particular product you get from the reactants compared to the maximum theoretical amount that you can get:

                                Actual Yield

Percentage Yield = ———————————

                                 Theoretical Yield

• Where actual yield is the number of moles or mass of product obtained experimentally.

• The predicted yield is the number of moles or mass obtained by calculation.

• You will often have to use the following equation to work out the reacting masses, to calculate the predicted yield.

                            Mass of a substance in grams (g)

Number of mol = ———————————————————

                            Molar mass (g mol¯¹)

• It is important to be clear about the type of particle you are referring to when dealing with moles.

  • Eg. 1 mole of CaF₂ contains one mole of CaF₂ formula units, but one mole of Ca²⁺ and two moles of F^- ions.