Percentage Yield

Percentage yield compares actual and theoretical yield

• The amount of product you get is known as the yield
• The more reactants you start with, the higher the actual yield will be
  • But the percentage yield doesn’t depend on the amount of reactants you started with, it’s a percentage
  • Percentage yield = mass of product actually made(g) / maximum theoretical mass of product x 100
  • Maximum theoretical mass can be calculated using balanced reaction equation
• Percentage yield is always somewhere between 0 and 100%
• 100% yield means that you get all the product you expected to get
• 0% yield means that no reactants were converted into products
• Industrial processes should have as high a percentage yield as possible to reduce waste and reduce costs

Yield are always less than 100%

• In real life, you never get a 100% yield
• Some products or reactant always gets lost along the way, and that goes fr big industrial process as well as school lab experiments
• Depends on what sort of reaction it is and what apparatus is being used

Not all reactants react to make a product

• In reversible reactions the products can turn back into reactant so the yield will never be 100%
  • For example, in the Haber process at the same time as the reaction N2 + 3H2 - 2NH3 is taking place, the reverse reaction is also happening
  • This means it never goes to completion