Stoichiometry: The Mole & Molecular Mass (CHM 30 Chapter 3) - Vocabulary

Vocabulary flashcards covering key terms from the lecture notes on stoichiometry: the mole concept, molecular mass, balancing equations, stoichiometric calculations, empirical/molecular formulas, combustion analysis, and limiting reactants.

Mole

The amount of substance containing 6.022 × 10^23 characteristic particles (atoms, molecules, etc.).

Avogadro’s number (NA)

6.022 × 10^23 particles per mole; units are mol⁻¹.

Diatomic elements

Elements that naturally exist as two-atom molecules (H2, N2, O2, F2, Cl2, Br2, I2).

Molar mass

Mass of one mole of a substance; units: g/mol; numerically equal to molecular mass.

Molecular mass

Sum of atomic masses in a molecule; measured in amu; numerically equal to molar mass (g/mol).

Atomic mass unit (amu)

Unit for atomic-scale masses; 1 u = 1/12 the mass of a carbon-12 atom.

CO2 molar mass

44.01 g/mol.

Balanced chemical equation

An equation with equal numbers of each type of atom on both sides, using the smallest whole-number coefficients; subscripts are not changed.

Coefficient

The number in front of a formula in a balanced equation that scales the amount of that substance.

State symbols

s, ℓ, g, and aq indicating solid, liquid, gas, or aqueous.

Mole-to-mole ratio

The ratio of amounts in moles from the coefficients in a balanced equation, used to convert between reactants and products.

Stoichiometry

The calculation of quantities of reactants and products in a chemical reaction using a balanced equation and molar masses.

Theoretical yield

The maximum amount of product that can be formed from the given reactants.

Actual yield

The amount of product actually obtained in an experiment.

Percent yield

(Actual yield / Theoretical yield) × 100%; cannot exceed 100%.

Limiting reactant

The reactant that limits the amount of product formed; determines the theoretical yield.

Excess reactant

The reactant that remains after the reaction goes to completion; present in excess.

Empirical formula

The smallest whole-number ratio of elements in a compound.

Molecular formula

The actual ratio of elements in a compound; a whole-number multiple of the empirical formula.

Empirical vs molecular formulas

Empirical is the lowest ratio; molecular is the actual ratio (a multiple of empirical).

Mass spectrometer M+ peak

The molecular ion peak that gives the compound’s molar mass.

Combustion

Reaction with oxygen; complete combustion of hydrocarbons yields CO2 and H2O.

Hydrocarbon

A compound containing only carbon and hydrogen.

Combustion analysis

Determining empirical formula by burning a compound and using CO2/H2O masses; mass difference reveals other elements.

Limiting reactant concept

The reactant that limits the maximum amount of product that can form in a reaction.