How much product you really get compared with the most you could, how many of the starting atoms end up in that product, and how industry weighs the two.
What you will learn
- Calculate percentage yield, including from a theoretical mass you work out
- Explain why yields are below 100%
- Calculate atom economy and compare routes to a product
Percentage yield
The theoretical yield is the most product the reactants could make, worked out from the equation.
The actual yield is what you collect.
percentage yield = mass of product actually made ÷ maximum theoretical mass × 100
All boards (Chemistry only): recall this.
- Heating 25.0 g of CaCO₃: theoretical mass of CaO = 25.0 ÷ 100 × 56 = 14.0 g
- actual mass collected = 11.9 g
- percentage yield = 11.9 ÷ 14.0 × 100 = 85.0%
Yields fall below 100% because:
- the reaction may be reversible, so it never goes to completion
- some product is lost when it is filtered, poured or dried
- some reactants take part in side reactions that make other products
To plan for a yield, work backwards. You need 18 g of product and the yield is 90%, so aim for a theoretical mass of 18 ÷ 0.90 = 20 g, then use reacting masses to find how much reactant makes 20 g.
The rest of this lesson and its 12 practice questions are locked.
In this lesson
- Percentage yield
- Atom economy
- Choosing a route
- Try it: Your first percentage yield
12 practice questions, marked as you go; about 20 minutes in all.
Key terms
Theoretical yield, Actual yield, Reversible, Lost, Side reactions
In this unit: Quantitative chemistry and the mole
Conservation of mass, relative formula mass, percentages and concentrations, the mole, reacting masses, empirical formulae, yield, atom economy, titrations and gas volumes.