# Theoretical yield

The is the maximum possible of a that can be made in a chemical reaction.

It can be calculated from:

• the
• the mass and of the , and
• the relative formula mass of the product

An is the mass of a product actually obtained from the reaction. It is usually less than the theoretical yield. The reasons for this include:

• incomplete reactions, in which some of the do not react to form the product
• practical losses during the experiment, such as during pouring or
• side reactions (unwanted reactions that compete with the desired reaction)
• in reactants

## Calculating theoretical yield

Reacting masses may be used to calculate the theoretical yield. Theoretical yield can also be worked out using a calculation.

### Worked example

If heated, calcium oxide to form calcium oxide and carbon dioxide.

Calculate the maximum theoretical yield of calcium oxide that can be produced from 250 g of calcium carbonate.

1. Write down the balanced chemical equation:
• CaCO3 CaO + CO2
2. Calculate the relative formula masses of the substances in the question:
• Mr of CaCO3 = 40.1 + 12.0 + (3 × 16.0) = 100.1
• Mr of CaO = 40.1 + 16.0 = 56.1
3. Use the balanced chemical equation to work out the reacting masses based on the relative formula masses:
• 100.1 g CaCO3 produces 56.1 g of CaO
4. Work out the reacting masses for 1 g (or 1 kg or 1 tonne if different mass units are used):
• = 1 g of CaCO3 produces g of CaO
5. Scale up the reacting masses to match the given reacting mass of the reactant:
• 250 g of CaCO3 produces x 250
• = 140 g of CaO