Stoichiometry and Related Calculations

Vocabulary flashcards covering core stoichiometry concepts, calculations, and terminology from the lecture notes.

Stoichiometry

The branch of chemistry that deals with quantitative relationships of reactants and products in a chemical reaction.

Molecular formula

Shows the actual number and type of each atom in a single molecule of a compound.

Empirical formula

Gives the simplest whole-number ratio of the different atoms or ions present in a compound.

Valency

The combining power of an element, often equal to its group number charge (e.g., Group I = 1+, Group VI = 2-).

Ball-and-stick model method

Find a compound’s formula by counting each type of atom in the molecular model.

Ion charge-swapping method

Write ion charges, swap the valencies, and use them as subscripts to obtain an ionic compound’s empirical formula.

State symbol (s)

Indicates a substance is in the solid state in a chemical equation.

State symbol (l)

Indicates a substance is in the liquid state in a chemical equation.

State symbol (g)

Indicates a substance is in the gaseous state in a chemical equation.

State symbol (aq)

Shows a substance is dissolved in water (aqueous) in a chemical equation.

Word equation

An equation that names reactants and products in words, e.g., Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water.

Symbol equation

Uses chemical symbols and formulae; must be balanced so each element has the same number of atoms on both sides.

Coefficient (balancing)

A whole number placed in front of a formula in an equation to adjust the number of atoms without changing substances.

Spectator ion

An ion that appears unchanged on both sides of an ionic equation and is omitted from the net ionic equation.

Ionic equation

An equation showing only the ions and molecules directly involved in the reaction after spectator ions are removed.

Relative atomic mass (Aᵣ)

Average mass of an element’s isotopes compared to 1⁄12 of a ¹²C atom.

Relative molecular mass (Mᵣ)

The sum of the relative atomic masses of all atoms in a molecule.

Relative formula mass

The Mᵣ applied to ionic compounds that do not exist as discrete molecules.

Mole (mol)

The amount of substance containing 6.02 × 10²³ particles; links mass to number of particles.

Avogadro constant

6.02 × 10²³, the number of particles in exactly one mole of a substance.

Molar mass

Mass of one mole of a substance, numerically equal to its Aᵣ or Mᵣ in g mol⁻¹.

Molar gas volume

Volume occupied by one mole of any gas at room temperature and pressure, equal to 24 dm³.

Concentration (mol dm⁻³)

Amount of solute in moles divided by volume of solution in cubic decimetres.

cm³ to dm³ conversion

Divide the volume in cm³ by 1000 to obtain dm³.

dm³ to cm³ conversion

Multiply the volume in dm³ by 1000 to obtain cm³.

Empirical formula calculation

Divide each element’s mass/percentage by its Aᵣ and scale the smallest ratio to whole numbers.

Molecular formula calculation

Find the Mr of the empirical formula, divide the compound’s Mr by it, and multiply subscripts by this factor.

Percentage yield

Actual product obtained ÷ theoretical product × 100; accounts for losses and incomplete reactions.

Percentage composition by mass

Total Aᵣ of an element in the compound ÷ Mᵣ of compound × 100.

Percentage purity

Mass of pure substance ÷ total sample mass × 100.