- Chemical formula
- A representation showing the type and number of atoms in one formula unit of a substance. E.g. H₂O, NaCl, Fe₂O₃.
- Balanced equation
- A symbol equation in which the number of atoms of each element is the same on both sides of the arrow.
- Coefficient
- The large number placed in front of a formula in a balanced equation. E.g. in 2H₂O, the coefficient is 2 and means two molecules of water.
- State symbol
- Symbols added in brackets to show physical state: (s) solid, (l) liquid, (g) gas, (aq) aqueous.
- Conservation of mass
- In a chemical reaction, the total mass of the reactants equals the total mass of the products. No atoms are created or destroyed.
- Open system
- A system where matter (typically a gas) can enter or leave, causing an apparent change in measured mass.
- Closed system
- A system where no matter can enter or leave; total mass is constant throughout the reaction.
- Polyatomic ion
- An ion composed of two or more atoms covalently bonded, carrying an overall charge. E.g. SO₄²⁻, NO₃⁻.
This definitions covers Key Terms within Formulae, Equations and Conservation of Mass for GCSE Chemistry. Revise Formulae, Equations and Conservation of Mass in Quantitative Chemistry for GCSE Chemistry with 13 exam-style questions and 12 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 8 of 14 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Practice questions for Formulae, Equations and Conservation of Mass
Which of the following is the correct formula for oxygen gas?
Explain why mass is conserved in a chemical reaction.
Quick recall flashcards
State the law of conservation of mass.
In a chemical reaction, the total mass of the products equals the total mass of the reactants.
No atoms are created or destroyed — they are only rearranged.
Name the seven diatomic elements.
H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂
Mnemonic: Have No Fear Of Ice Cold Beer