Key Definitions
This definitions covers Key Definitions within Moles & Calculations for GCSE Chemistry. Revise Moles & Calculations in Quantitative Chemistry for GCSE Chemistry with 27 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 6 of 17 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 17
Practice
27 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.
Keep building this topic
Read this section alongside the surrounding pages in Moles & Calculations. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Moles & Calculations
One mole of any substance contains how many particles?
Explain why the percentage yield of a reaction is never 100% in practice.
Quick Recall Flashcards
27 questions on Moles & Calculations — practise free
Instant marking, adaptive difficulty, and 20 spaced repetition flashcards. Free until your GCSEs.
Try PrepWise Free