The reactant that completely reacts, thereby determining the maximum amount of product that can be formed in a chemical reaction. All other reactants will be present in excess.

Any reactant present in a greater amount than is necessary to completely react with the limiting reactant.

The maximum calculated mass of product expected to form from a given amount of reactants.

A mole of a substance contains 6.02 × 10²³ particles of it. The mass of one mole of a substance is its relative mass in grams.

The molar ratio of the reactants to the products in a chemical reaction.

Limiting reactants

Combined science

In the Making salts unit, pupils will learn about the production of pure salts, concentration and strength of acids, and what makes acids acidic and how bases can neutralise them.

In the Understanding Chemical Reactions unit, pupils learned about how atoms rearrange during chemical reactions and the conservation of mass.

Calculations involving masses

Physical activity and equipment requiring safe use

the reactant that completely reacts during a reaction

a reactant that is left over at the end of the reaction

the maximum calculated mass of product expected from a reaction

Match the following key terms to the correct definitions. 

One mole of hydrogen reacts with one mole of oxygen.

One mole of oxygen reacts with two moles of hydrogen.

Two moles of water are formed for every two moles of hydrogen reacted.

Two moles of oxygen are needed to form two moles of water.

Which of these statements about the equation are true?
2H₂ + O₂ → 2H₂O.

True or false? In a chemical reaction there are the same number of atoms in the products as there were in the reactants.

A student oxidises magnesium in a Bunsen burner flame. The oxygen is in excess.
2Mg + O₂ → 2MgO.
How many moles of magnesium oxide would form from eight moles of magnesium?

Which is the limiting reactant if 6 moles of methane reacts with 4 moles of oxygen?
CH₄ + 2O₂ → CO₂ + 2H₂O.

A student oxidises 2.0 g of magnesium in a Bunsen burner flame. The oxygen is in excess. 
2Mg + O₂ → 2MgO.
What mass of magnesium oxide would form from 2.0 g of magnesium? Give your answer to 2 s.f.

the average mass of the atoms of an element compared to carbon-12

the sum of the relative atomic masses of all the atoms in a formula

the number of particles in one mole of a substance

Match the following terms to the correct definition.

The ratio of nitrogen to oxygen is 2 : 3.

The ratio of nitrogen to hydrogen is 1 : 2.

The ratio of oxygen to hydrogen is 3 : 4. 

The ratio of oxygen to nitrogen is 2 : 3.

The formula for ammonium nitrate is NH₄NO₃. Which of the following ratios are correct?

Chemical equations represent how the atoms in the {{ }} rearrange to form the products.

mass = amount of substance × relative formula mass

mass = amount of substance ÷ relative formula mass

amount of substance = relative formula mass × mass

amount of substance = relative formula mass ÷ mass

Which of the following is the equation which links mass, relative formula mass and amount of substance?

True of false? The following equation is balanced:
C₂H₄ + 2O₂ → 2CO₂ + 2H₂O.

Calculate the relative formula mass for calcium carbonate, CaCO₃. Relative atomic masses: Ca = 40; C = 12; O = 16.

Content guidance

Risk assessment required - equipment

Adult supervision required

This lesson will be removed by end of Summer Term 2025.

Limiting reactants

Lesson outcome

Content guidance

This lesson will be removed by end of Summer Term 2025.