Stoichiometry refers to the molar ratio of the reactants and products in a chemical reaction.

The relative formula mass (RFM or Mᵣ) of a substance is the sum of the relative atomic masses of all the atoms in its formula.

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

A coefficient is the number placed in front of a chemical formula to balance an equation; it multiplies all the atoms in the formula and shows the ratio of substances in a reaction.

A balanced symbol equation represents a chemical reaction using symbols and coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.

Mass in a chemical reaction: using moles

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.

This unit covers writing chemical formulae, balancing equations, and using the conservation of mass. It includes calculating moles, empirical formulae, relative formula masses, and theoretical yields. Emphasis is on stoichiometry, concentration, gas volumes, and using standard form.

Calculations involving masses

Measuring elements and their ratios in reactions.

The temperature changes in chemical reactions.

What does stoichiometry mean in chemistry?

The physical states of the reactants and products.

How many particles are involved in the reaction.

The proportions of substances that react or are produced.

In a balanced chemical equation, what does the mole ratio of reactants and products tell us?

The {{}} is the sum of the relative atomic masses of all the atoms in a formula, representing the mass of a molecule relative to the mass of a carbon-12 atom.

Two molecules of hydrogen react with one molecule of oxygen.

Two moles of hydrogen are needed to react with one mole of oxygen.

Four hydrogen atoms react with two oxygen atoms.

2 hydrogens reacts with oxygen to make 2 lots of water.

Which of the following statements best describes what the equation 2H₂ + O₂ → 2H₂O tells us?

Given the reaction: CH₄ + 2O₂ → CO₂ + 2H₂O, how many grams of CO₂ are produced when 16 g of methane (CH₄) reacts completely? Relative formula mass values: (CH₄ = 16) & (CO₂ = 44)

Using the reaction: N₂ + 3H₂ → 2NH₃, calculate the mass of ammonia (NH₃) produced when 14 g of nitrogen react with hydrogen? (2 s.f.)
Relative formula mass values: (N₂ = 28) & (NH₃ = 17)

Given the relative atomic masses (Ar): C (12), O (16)
Calculate the relative molecular mass (Mr) of carbon dioxide (CO₂).

Mass of products is always more than the mass of reactants.

Mass of reactants is converted into energy.

Mass of reactants equals mass of products.

What does the conservation of mass in a chemical reaction imply?

If 20 g of sodium reacts fully with 15 g of chlorine, how much sodium chloride is produced?

For the equation __ N₂ + __ H₂ → __ NH₃, select the correct coefficients to balance it.

Two molecules of hydrogen react with two molecules of oxygen.

One molecule of hydrogen reacts with one molecule of oxygen.

Two molecules of water are decomposed into hydrogen and oxygen.

What does the equation 2H₂ + O₂ → 2H₂O tell us?

Given the relative atomic mass values (Ar): H (1), S (32), O (16)
Calculate the relative formula mass (Mr) of sulfuric acid.

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

Mass in a chemical reaction: using moles

Lesson outcome

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