This definitions covers Key Definitions within Moles & Calculations for GCSE Chemistry. Revise Moles & Calculations in Quantitative Chemistry for GCSE Chemistry with 22 exam-style questions and 20 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 6 of 15 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Topic position
Section 6 of 15
Practice
22 questions
Recall
20 flashcards
📖 Key Definitions
Mole (mol): The unit chemists use to count particles. One mole contains 6.02 × 10²³ particles (atoms, molecules, or ions).
Avogadro's constant: 6.02 × 10²³ particles per mole — the number of atoms in exactly 12 g of carbon-12.
Relative formula mass (Mr): The sum of all relative atomic masses in a compound. It has no units.
Percentage yield: (actual yield ÷ theoretical yield) × 100. Measures how close a real reaction gets to the theoretical maximum.
Atom economy: (Mr of desired product ÷ total Mr of all products) × 100. A measure of how efficiently atoms are used — higher is greener.
Conservation of mass: The total mass of reactants equals the total mass of products in any chemical reaction, because atoms are neither created nor destroyed.