Essential IGCSE Chemistry Equations and Formulas: Quick Review Sheet

Mastering the IGCSE chemistry equations list is one of the highest-leverage things you can do before the exam. Mathematical questions appear across multiple paper sections, and a single forgotten formula can cost marks on an entire multi-part question.

The equations list is the set of relationships you apply to calculate moles, masses, gas volumes, concentrations, and energy changes across Cambridge, Edexcel, and AQA. Knowing them by heart, with the correct units, separates a Grade 7 paper from a Grade 9.

Why do chemistry equations matter?

Mathematical questions make up a significant share of the marks in IGCSE Chemistry, so a handful of core formulas directly affects your grade. Recall and correct application are what turn understanding into marks.

Our tutors regularly see students drop marks not because they misunderstand the chemistry, but because they confuse units, forget to convert, or apply the wrong equation. The fix is systematic memorisation combined with backward-calculation practice.

Forgetting a single step in a mole calculation can invalidate every later part of a question. Examiners award method marks, so showing your working is always worth doing, even when your final answer is wrong.

The essential equations

The table below covers the core mathematical relationships tested in IGCSE Chemistry. They appear across stoichiometry, gas-volume, and solution-concentration questions at Cambridge, Edexcel, and AQA level.

Target Value	Equation	Units
Moles from mass	Moles = Mass divided by relative formula mass (Mr)	Mass in grams; Mr is dimensionless
Mass from moles	Mass = Moles multiplied by relative formula mass (Mr)	Measured strictly in grams
Gas volumes (RTP)	Volume = Moles multiplied by 24 dm³	Decimetres cubed (dm³)
Solution concentration	Concentration = Moles divided by volume of solution	Expressed as mol/dm³
Moles from concentration	Moles = Concentration multiplied by volume	Volume must be in dm³
Percentage yield	Percentage yield = (Actual yield / Theoretical yield) × 100	Expressed as a percentage (%)
Atom economy	Atom economy = (Mr desired product / total Mr products) × 100	Expressed as a percentage (%)

Always convert cm³ volumes into dm³ before any concentration calculation: divide by 1,000, so 250 cm³ becomes 0.25 dm³. Show every conversion step to claim partial marks if your final answer slips.

Moles, gas volumes, and concentration

Calculating moles

The mole calculation is the foundation of IGCSE stoichiometry. Every mass, volume, and concentration question traces back to this single relationship.

To calculate moles from a mass, divide the mass in grams by the relative formula mass (Mr). The Mr is the sum of the relative atomic masses of all atoms in the formula, read from your periodic table.

A simple triangle helps recall: Mass at the top, Moles and Mr at the bottom. Cover the value you want, and the triangle shows the operation. If a question gives mass and asks for moles, divide; if it gives moles, multiply.

Students who begin IGCSE tutoring early in Year 10 usually find mole calculations become automatic well before the exam. That frees mental bandwidth for the harder multi-step questions that follow.

Gas volumes

Gas-volume calculations use a fixed molar volume at room temperature and pressure (RTP). At RTP, one mole of any gas occupies 24 dm³. The equation is Volume (dm³) = Moles × 24; rearranged, Moles = Volume ÷ 24.

This applies to all gases regardless of identity, which makes it one of the more forgiving formulas. In Cambridge papers, gas-volume questions often appear as the second or third part of a multi-step stoichiometry question.

The most frequent mistake is using 24,000 cm³ instead of 24 dm³ without checking what the question asks for. Read the unit on the answer line before you calculate, and convert if needed.

Concentration and molarity

Concentration (mol/dm³) equals moles divided by volume in dm³. The three-way relationship works like the mole triangle: cover any one of concentration, moles, or volume, and the other two show the operation.

Rearranged: Moles = Concentration × Volume, and Volume = Moles ÷ Concentration. Titration questions are a reliable source of marks because the method is consistent: find moles first, then divide by volume to get the unknown concentration.

Every volume in a concentration calculation must be in dm³ before you apply the formula. Questions almost always give volumes in cm³ to test whether you remember to divide by 1,000, so check it every time.

Yield, atom economy, and energy

Percentage yield

Percentage yield compares how much product you actually obtained against the theoretical maximum: (Actual yield ÷ Theoretical yield) × 100. A result below 100% reflects real losses from incomplete reactions, evaporation, or filtration.

Atom economy

Atom economy measures how efficiently a reaction uses its starting materials: (Mr of desired product ÷ total Mr of all products) × 100. Higher atom economy means less waste, which is why AQA and Cambridge test it in green-chemistry contexts.

Energy changes

For thermochemistry, use Energy (J) = Mass (g) × Specific heat capacity × Temperature change. The specific heat capacity of water, 4.18 J/g°C, is usually provided, but knowing it saves time.

Bond-enthalpy calculations use a simple rule: energy in (bonds broken) minus energy out (bonds formed) equals the overall energy change. A negative result means the reaction is exothermic.

Before the exam: checklist and support

Quick revision checklist

In the week before your chemistry paper, these high-priority actions target the calculation marks most students leave on the table:

• Memorise metric unit conversions
• Drill backward mole calculations to catch errors
• Convert cm³ to dm³ in every concentration question
• Write percentage yield and atom economy from memory
• Check the unit on the answer line first
• Show all working, even obvious steps

How Talimat can help

Working through an equations list on paper is one thing; applying it under timed exam conditions is another. That is where structured IGCSE tutoring makes a measurable difference.

At Talimat, every student is matched with a subject-specialist tutor who holds a relevant degree. Live 1:1 sessions let the tutor spot exactly which equations a student misapplies and correct the habit before it costs marks.

The platform also includes mock exams with detailed feedback, a parent dashboard, and a dedicated Academic Consultant from day one. If your child needs targeted support with calculation questions, contact us to be matched with a chemistry tutor.

None of this takes long, but doing it consistently in the days before the exam builds the automaticity that keeps calculation errors out of your paper. Pair this guide with past-paper practice and you will hold onto marks others lose.