A-Level Chemistry calculations & formulae
AQA / Edexcel / OCR A-Level Chemistry
The core calculations you must be fluent in for A-Level Chemistry, with the formula, what each term means and the units.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Amount of substance
| In words | Symbols | Quantities & units |
|---|---|---|
| moles = mass ÷ molar mass | n = m ÷ M | n (mol), m (g), M (g/mol) |
| moles = concentration × volume | n = c × V | n (mol), c (mol/dm³), V (dm³) |
| moles of gas = volume ÷ molar volume (RTP) | n = V ÷ 24 000 | V (cm³) at RTP; or ÷24 for dm³ |
| ideal gas equation | p V = n R T | p (Pa), V (m³), n (mol), R = 8.31, T (K) |
Yield & atom economy
| In words | Symbols | Quantities & units |
|---|---|---|
| percentage yield = (actual ÷ theoretical) × 100 | % yield = actual/theoretical × 100 | mass or moles |
| atom economy = (Mr of desired product ÷ Mr of all reactants) × 100 | % atom economy | from the balanced equation |
Energetics & equilibria
| In words | Symbols | Quantities & units |
|---|---|---|
| enthalpy change = mass × specific heat capacity × temperature change | q = m c ΔT | q (J), m (g), c (4.18 J/g°C), ΔT (°C) |
| pH | pH = −log₁₀[H⁺] | [H⁺] in mol/dm³ |
| hydrogen ion concentration | [H⁺] = 10^(−pH) | mol/dm³ |
▶ Practise a calculation question and get it marked (free) →