TOPIC 3: STOICHIOMETRY

Relative atomic mass (Ar)

Weighted average mass of isotopes compared to carbon-12

Relative molecular mass (Mr)

Sum of relative atomic masses of all atoms in a molecule

Mole definition

Amount of substance containing 6.02 × 10^23 particles

Avogadro constant

6.02 × 10^23 particles per mole

Mole calculation (mass)

Mass= moles x molar mass

Mole calculation

Moles = mass ÷ molar mass

Balanced equation

Must have same number of each type of atom on both sides

Stoichiometry definition

Using mole ratios from balanced equations to calculate quantities

Steps in mole calculations

Write equation, balance it, calculate moles, use ratio, convert to required unit

Concentration

Amount of solute per volume of solution

Concentration formula

Concentration = moles ÷ volume (dm³)

Gas volume at rtp

1 mole of gas occupies 24 dm³ at room temperature and pressure

Gas calculation

Moles = volume ÷ 24

Limiting reagent

Reactant that is completely used up and limits amount of product formed

Excess reagent

Reactant that remains after reaction

Percentage yield

(actual yield ÷ theoretical yield) × 100

Empirical formula

Simplest whole number ratio of atoms in a compound

Molecular formula

Actual number of atoms in a molecule