A word equation represents a chemical reaction using the chemical names of the reactants and products.

A chemical formula represents a substance using element symbols and the number / ratio of atoms of each element in the substance.

A symbol equation represents a chemical reaction using the chemical formulas of the reactants and products.

A balanced symbol equation uses coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.

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.

Balancing equations

Combined science

Three types of chemical reaction

Conservation of mass

Uncertainties in measurements: chemistry

Mass in a chemical reaction

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

number and ratio of each element in a substance

What does a chemical formula like Na₂O represent?

describes a chemical reaction using chemical names

represents a substance using element symbols and numbers

describes chemical reactions using chemical formulae and state symbols

Match the terms to the correct definitions. 

Identify the reactants' and products' chemical formulae.

Count the initial particles of each type in the reactants and products.

Add coefficients to each substance to add multiples, as required. 

Confirm the final number of particles in the reactants is equal to the products.

Starting with identifying the reactants and products chemical formulae, sort the steps to describe how to balance an equation.

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

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

Cl₂ (l) + KI (aq) → KCl (aq) + I₂ (l)

NaOH (aq) + HNO₃ (aq) → NaNO₃ (aq) + H₂O (l)

C₃H₈ (g) + O₂ (g) -> CO₂ (g) + H₂O (g)

C₃H₈ (g) + 2O₂ (g) -> 3CO₂ (g) + 4H₂O (g)

C₃H₈ (g) + 5O₂ (g) -> 3CO₂ (g) + 4H₂O (l)

2C₃H₈ (g) + 7O₂ (g) -> 6CO (g) + 8H₂O (g)

C₃H₈ (g) + 5O₂ (g) -> 3CO₂ (g) + 4H₂O (g)

Select the correct balanced equation for when propane (C₃H₈) completely combusts to form carbon dioxide and steam.

What elements are present in CaCO₃ and how many atoms are there of each?

Match the substance names and symbol formulae. 

Match the substance to the correct state symbol.

The chemical formula for magnesium oxide is MgO. In a chemical symbol equation, how would you amend this to provide twice as many Mg and O particles?

When 12.2 g of iron reacted with an unknown mass of sulfur, 20.6 g of a product was formed. What was the mass of the sulfur? 

Br₂ (g) + 2NaI (aq) → 2NaBr (aq) + I₂ (g)

Br₂ (aq) + 2NaI (aq) → 2NaBr (aq) + I₂ (aq)

Br₂ (l) + NaI (aq) → NaBr (aq) + I₂ (l)

Which symbol equation is correct for when bromine displaces iodine from sodium iodide solution?

Balancing equations

Lesson outcome