Ch. 5 Chemical Formulae, Equations and Calculations – Part 1

Vocabulary flashcards summarising essential terms and definitions for chemical formulae, equations, and calculation topics.

Word Equation

A chemical equation written with reactant and product names, e.g. Magnesium + oxygen → magnesium oxide.

Chemical (Symbol) Equation

A chemical reaction expressed with chemical formulae and stoichiometric coefficients, e.g. 2 Mg + O₂ → 2 MgO.

State Symbols

Letters in brackets that show the physical state of substances in an equation: (s) solid, (l) liquid, (g) gas, (aq) aqueous.

Balancing an Equation

Adjusting coefficients so the number of atoms of each element is equal on both sides of a chemical equation.

Relative Atomic Mass (Aᵣ)

The weighted average mass of the isotopes of an element compared with 1⁄12 of the mass of a carbon-12 atom.

Relative Formula Mass (Mᵣ)

The sum of the relative atomic masses of all atoms in a compound’s formula.

Mole (Amount of Substance)

SI unit that contains 6.02 × 10²³ particles; 1 mol of any substance has a mass equal to its Mᵣ in grams.

Mole Formula

Number of moles = mass (g) ÷ Mᵣ.

Reacting Masses

Quantities of reactants or products calculated from a balanced equation and molar relationships.

Yield

The actual mass of product obtained from a reaction.

Percentage Yield

(Actual yield ÷ Theoretical yield) × 100; measures reaction efficiency.

Purity

The extent to which a substance is free from other substances; impurities may be harmful.

Empirical Formula

The simplest whole-number ratio of atoms of each element in a compound.

Molecular Formula

The actual number of atoms of each element present in one molecule of a compound.

Empirical Formula Mass

Total relative atomic mass of the atoms in an empirical formula.

Limiting Reactant

The reactant that is completely used up first, thus limiting the amount of product formed.

Excess Reactant

A reactant present in more than the amount needed to react completely with the limiting reactant.

Combustion Method (MgO)

Practical technique where magnesium is burned in air; mass changes are used to deduce the empirical formula of magnesium oxide.

Reduction Method (CuO)

Practical technique where copper(II) oxide is heated in a stream of hydrogen; loss in mass reveals oxygen removed and leads to the formula CuO.

Water of Crystallization

Chemically bound water molecules within a crystalline salt, determinable by heating or reduction experiments.

Stoichiometry

The quantitative relationship between reactants and products in a balanced chemical equation.