A scale from 0-14 measuring acidity/alkalinity. pH 7 = alkali.

Chemical Changes - AQA GCSE Chemistry Revision

Topic overview

What you need to know

Chemical Changes is a key part of GCSE Chemistry. Link particles, structure and energy changes to the observations and calculations you may be given. The gain of oxygen or loss of electrons. In terms of electrons: OIL (Oxidation Is Loss). The loss of oxygen or gain of electrons. In terms of electrons: RIG (Reduction Is Gain). A list of metals in order of reactivity: K, Na, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au (most to least reactive).

Exam tip

Balance equations, show units in calculations and connect macroscopic observations to particles.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

Oxidation: The gain of oxygen or loss of electrons. In terms of electrons: OIL (Oxidation Is Loss).
Reduction: The loss of oxygen or gain of electrons. In terms of electrons: RIG (Reduction Is Gain).
Reactivity Series: A list of metals in order of reactivity: K, Na, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au (most to least reactive).
Displacement Reaction: A more reactive element displaces a less reactive one from its compound. E.g. Zn + CuSO₄ → ZnSO₄ + Cu.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

Electrolysis: Using electricity to decompose an ionic compound (molten or in solution). Positive ions go to the cathode (−), negative ions to the anode (+).
pH Scale: A scale from 0-14 measuring acidity/alkalinity. pH < 7 = acid, pH 7 = neutral, pH > 7 = alkali.
Neutralisation: Acid + alkali → salt + water. The H⁺ ions react with OH⁻ ions to form water: H⁺ + OH⁻ → H₂O.
Strong vs Weak Acid: Strong acids fully ionise in water (e.g. HCl, H₂SO₄). Weak acids only partially ionise (e.g. ethanoic acid, citric acid).

Core knowledge

Key facts for Chemical Changes

8 essentials

Oxidation

The gain of oxygen or loss of electrons. In terms of electrons: OIL (Oxidation Is Loss).

Reduction

The loss of oxygen or gain of electrons. In terms of electrons: RIG (Reduction Is Gain).

Reactivity Series

A list of metals in order of reactivity: K, Na, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au (most to least reactive).

Displacement Reaction

A more reactive element displaces a less reactive one from its compound. E.g. Zn + CuSO₄ → ZnSO₄ + Cu.

Electrolysis

Using electricity to decompose an ionic compound (molten or in solution). Positive ions go to the cathode (−), negative ions to the anode (+).

pH Scale

A scale from 0-14 measuring acidity/alkalinity. pH < 7 = acid, pH 7 = neutral, pH > 7 = alkali.

Neutralisation

Acid + alkali → salt + water. The H⁺ ions react with OH⁻ ions to form water: H⁺ + OH⁻ → H₂O.

Strong vs Weak Acid

Strong acids fully ionise in water (e.g. HCl, H₂SO₄). Weak acids only partially ionise (e.g. ethanoic acid, citric acid).

Active recall

Close the notes and answer these

1.Without looking, explain oxidation and give one example or consequence.
2.Without looking, explain reduction and give one example or consequence.
3.Without looking, explain reactivity series and give one example or consequence.
4.Without looking, explain displacement reaction and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

Mark the notes complete, then test what you can recall.

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