How to memorise chemistry equations for SPM

There are a lot of equations in SPM Chemistry, and trying to memorise each one as an isolated string of symbols is exhausting and unreliable, under exam pressure, blindly memorised equations blur together and fall apart. The good news is that you do not need to memorise nearly as many as you think. Most equations are examples of a handful of reaction patterns, and once you know the patterns and can balance, you can reconstruct almost any equation on the spot. This guide shows you how.

Understand before you memorise

An equation you understand is one you can rebuild if you forget it; an equation you have only memorised is gone the moment your memory slips. Before drilling any reaction, make sure you can answer three questions about it: what type of reaction is this, what are the products, and why. For example, “acid + metal” always gives a salt and hydrogen gas. Once that pattern is in your head, you do not memorise Mg + 2HCl → MgCl₂ + H₂ as a random fact, you derive it: magnesium is the metal, hydrochloric acid the acid, so the products must be magnesium chloride (the salt) and hydrogen. Understanding turns dozens of separate equations into a few reliable rules.

Learn the reaction patterns, not the equations

Group the syllabus reactions into their families and learn one clear example of each. The big ones to know cold:

• Acid + metal → salt + hydrogen. e.g. Mg + 2HCl → MgCl₂ + H₂
• Acid + base/metal oxide → salt + water. e.g. CuO + H₂SO₄ → CuSO₄ + H₂O
• Acid + metal carbonate → salt + water + carbon dioxide. e.g. 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
• Neutralisation (acid + alkali) → salt + water. e.g. HCl + NaOH → NaCl + H₂O
• Combustion of a hydrocarbon → carbon dioxide + water. e.g. CH₄ + 2O₂ → CO₂ + 2H₂O
• Displacement (more reactive metal displaces a less reactive one). e.g. Zn + CuSO₄ → ZnSO₄ + Cu
• Thermal decomposition of a carbonate → metal oxide + carbon dioxide. e.g. CaCO₃ → CaO + CO₂

Once these patterns are second nature, a new question is not a new equation to recall, it is one of these families with different names slotted in. The reactions reference is a good place to see the families laid out together, and the reaction chemistry of acids, bases and salts is where several of these patterns live in the syllabus.

Balancing is the skill that makes recall optional

If you can balance confidently, you never need to memorise the numbers in front of each formula, you can always work them out. The method is simple and worth drilling until it is automatic:

1. Write the correct formulae for every reactant and product (this part you do need to know, the formula of sulfuric acid is H₂SO₄, not HSO₄).
2. Count each type of atom on both sides.
3. Adjust the big coefficients (never the small subscripts) until every atom balances.
4. Check gas molecules like O₂ and H₂ last, and re-count.

For example, to balance the reaction of magnesium with hydrochloric acid: write Mg + HCl → MgCl₂ + H₂. Chlorine is unbalanced (1 on the left, 2 on the right), so put a 2 in front of HCl: Mg + 2HCl → MgCl₂ + H₂. Now magnesium, chlorine and hydrogen all balance. Practise this until it takes seconds. You can check your work with an equation balancer while you build the skill, but the goal is to do it yourself in the exam.

Use active recall, not passive rereading

Rereading a list of equations feels productive and barely works. What works is retrieving them from a blank page. Try this: write the reactant side only, close your notes, and complete and balance the equation from memory. Then check. The struggle to recall is exactly what builds the memory, passively reading the finished equation does almost nothing by comparison. Flashcards suit this well: reactants on the front, full balanced equation with state symbols on the back.

Space it out and include state symbols

Cramming all the equations the night before is the least effective method there is. Reviewing a few each day, coming back to the ones you get wrong more often, embeds them far more durably, this is spaced repetition, and it genuinely works. As you drill, include the state symbols (s), (l), (g) and (aq) from the start, because SPM often wants them and they are easy marks to drop. For ionic reactions, learn the ionic equation too: neutralisation, at heart, is always H⁺ + OH⁻ → H₂O, and precipitation is just the two ions that combine, such as Ag⁺ + Cl⁻ → AgCl.

Put it together

Memorising equations for SPM is really three smaller skills working together: knowing the reaction patterns, being able to balance, and testing yourself by active recall rather than rereading. Do those three, spaced across your revision, and the mountain of equations shrinks to a short list of rules you can apply to anything the exam puts in front of you.