Amount of substance key terms

Relative atomic mass

The mass of one atom of an element expressed in atomic mass units (u), defined relative to the mass of a carbon‑12 atom.

Isotopic mass

The mass of a specific isotope of an element, measured in atomic mass units.

Relative atomic mass

The weighted average mass of an atom of an element compared to 1/12th the mass of a carbon-12 atom.

Relative molecular mass

The mass of a molecule compared to 1/12th the mass of a carbon-12 atom.

Molar mass

The mass of one mole of a substance, typically expressed in grams per mole (g/mol).

Stoichiometry

The calculation of reactants and products in chemical reactions based on the conservation of mass.

Relative atomic mass

The weighted average mass of the naturally occurring isotopes of an element, expressed in atomic mass units (u).

Relative molecular mass

The sum of the relative atomic masses of all atoms in a molecule, expressed in atomic mass units (u).

Avogadro constant

The number of elementary entities in one mole of a substance, 6.022×10^23 mol^−1.

Mole

The amount of substance that contains as many elementary entities as there are atoms in 12 g of carbon‑12.

Avogadro’s constant

The number of entities (atoms, molecules, ions, or formula units) in one mole of a substance, equal to 6.022 × 10²³ mol⁻¹.

Formula unit

The smallest repeating unit in an ionic compound that represents the stoichiometry of the compound, e.g., NaCl.

Mole

A mole is the amount of substance that contains as many entities (atoms, molecules, etc.) as there are in 12 grams of carbon-12.

Avogadro's constant

Avogadro's constant is the number of particles in one mole of a substance, approximately 6.02 × 10^23.

Mole

A mole is the amount of substance that contains as many entities (atoms, molecules, etc.) as there are in 12 grams of carbon-12.

Molar Mass

The mass of one mole of a substance, typically expressed in grams per mole (g/mol).

Concentration

The amount of solute present in a given volume of solution, typically expressed in mol/dm³.

Mole

A unit of measurement in chemistry that represents 6.022 x 10²³ entities (atoms, molecules, ions, etc.).

Mole

The amount of substance that contains 6.022×10^23 entities, linking mass to number of particles.

Avogadro constant

The number of entities in one mole, 6.022×10^23 mol^−1.

Ideal Gas

A hypothetical gas that perfectly follows the ideal gas law, with no intermolecular forces and occupying no volume.

Molar Volume

The volume occupied by one mole of a gas at standard temperature and pressure (STP), approximately 22.4 L.

Ideal gas equation

The relationship PV = nRT that describes the behaviour of an ideal gas, where P is pressure, V is volume, n is amount of substance, R is the gas constant and T is temperature in Kelvin.

Gas constant (R)

A universal constant that relates the energy scale of a gas to its pressure, volume, amount and temperature. Its value depends on the units used: 8.314 J mol⁻¹ K⁻¹ (SI) or 0.0821 L atm mol⁻¹ K⁻¹.

Ideal Gas

A hypothetical gas that perfectly follows the ideal gas law, with no interactions between particles and occupying no volume.

Mole

The amount of substance that contains as many entities (atoms, molecules, etc.) as there are in 12 grams of carbon-12.

Ideal gas equation

The relationship PV = nRT linking pressure, volume, temperature, amount of gas, and the ideal gas constant R.

Unit consistency

Ensuring all quantities in an equation are expressed in compatible units so that the calculation yields a physically meaningful result.

Molar Mass

The mass of one mole of a substance, typically expressed in grams per mole (g/mol).

Stoichiometry

The calculation of reactants and products in chemical reactions based on the conservation of mass.